14. HTTP bindings#

Smithy provides various HTTP binding traits that can be used by protocols to explicitly configure HTTP request and response messages.

The members of an operation input, output, and errors MUST NOT be bound to multiple HTTP message locations (e.g., a member cannot be bound to both a URI label and to a header). Only top-level members of an operation's input, output, and error structures are considered when serializing HTTP messages.

Important

Violating HTTP specifications or relying on poorly-supported HTTP functionality when defining HTTP bindings will limit interoperability and likely lead to undefined behavior across Smithy implementations. For example, avoid defining GET/DELETE requests with payloads, defining response payloads for operations with a 204/205 status, etc.

14.1. `http` trait#

Summary: Configures the HTTP bindings of an operation.
Trait selector: operation
Value type: structure

The http trait is a structure that supports the following members:

Property	Type	Description
method	`string`	Required. The HTTP method of the operation.
uri	`string`	Required. The URI pattern of the operation. Labels defined in the URI pattern are used to bind operation input members to the URI.
code	`integer`	The HTTP status code of a successful response. Defaults to `200` if not provided. The provided value SHOULD be between 200 and 299, and it MUST be between 100 and 999. Status codes that do not allow a body like 204 and 205 SHOULD bind all output members to locations other than the body of the response.

The following example defines an operation that uses HTTP bindings:

$version: "2"
namespace smithy.example

@idempotent
@http(method: "PUT", uri: "/{bucketName}/{key}", code: 200)
operation PutObject {
    input: PutObjectInput
}

@input
structure PutObjectInput {
    // Sent in the URI label named "key".
    @required
    @httpLabel
    key: ObjectKey

    // Sent in the URI label named "bucketName".
    @required
    @httpLabel
    bucketName: String

    // Sent in the X-Foo header
    @httpHeader("X-Foo")
    foo: String

    // Sent in the query string as paramName
    @httpQuery("paramName")
    someValue: String

    // Sent in the body
    data: MyBlob

    // Sent in the body
    additional: String
}

14.1.1. method#

The method property defines the HTTP method of the operation (e.g., "GET", "PUT", "POST", "DELETE", "PATCH", etc). Smithy will use this value literally and will perform no validation on the method. The method value SHOULD match one of the definitions found in RFC 9110#section-9.3. This property does not influence the safety or idempotency characteristics of an operation.

14.1.2. uri#

The uri property defines the request-target of the operation in origin-form as defined in RFC 9112#section-3.2.1. The URI is a simple pattern that Smithy uses to match HTTP requests to operations and to bind components of the request URI to fields in the operations's input structure. Patterns consist of literal characters that MUST be matched in the request URI and labels which are used to insert named components into the request URI.

The resolved absolute URI of an operation is formed by combining the URI of the operation with the endpoint of the service. (that is, the host and any base URL of where the service is deployed). For example, given a service endpoint of https://example.com/v1 and an operation pattern of /myresource, the resolved absolute URI of the operation is https://example.com/v1/myresource.

The value provided for the uri property MUST adhere to the following constraints:

MUST start with "/".
MUST NOT contain empty path segments (i.e., "//").
MUST NOT contain a fragment (i.e., "#").
MUST NOT end with "?".
MUST NOT contain dot-segments (i.e., ".." and ".").
MUST NOT case-sensitively conflict with other http / uri properties.

@readonly
@http(method: "GET", uri: "/foo/{baz}")
operation GetService {
    output: GetServiceOutput
}

14.1.2.1. Literal character sequences#

Patterns with no labels will match only requests containing the exact literal characters declared in the pattern, with the exception of trailing slashes which are always optional.

Given an endpoint of https://yourhost and a pattern of /my/uri/path:

Request URI	Matches?	Reason
`https://yourhost/my/uri/path`	Yes	Exact match
`https://yourhost/my/uri/path/`	Yes	Trailing slashes are ignored
`https://yourhost/my/uri`	No	Missing "/path"
`https://yourhost/my/uri/other`	No	Found "/other" instead of "/path"
`https://yourhost/my/uri/path/other`	No	Trailing segment "/other"

14.1.2.2. Labels#

Patterns MAY contain label placeholders in the path. Labels consist of label name characters surrounded by open and closed braces (i.e., "{label_name}" is a label and label_name is the label name). The label name corresponds to a top-level operation input structure member name. Every label MUST have a corresponding input member, the input member MUST be marked as required trait, the input member MUST have the httpLabel trait, and the input member MUST reference a string, byte, short, integer, long, float, double, bigDecimal, bigInteger, boolean, or timestamp. Labels only capture path segments.

Labels MUST adhere to the following constraints:

Labels MUST NOT appear in the query string.
Each label MUST span an entire path segment (e.g., "/{foo}/bar" is valid, and "/{foo}bar" is invalid).

A pattern of /my/uri/{label} will match any URI that begins with /my/uri/ followed by any string not including an additional path segment ("/").

Given a pattern of /my/uri/{label} and an endpoint of http://yourhost:

Request URI	Matches?	Reason
`http://yourhost/my/uri/foo`	Yes	"/my/uri/" matches and "foo" is captured as `label`.
`http://yourhost/my/uri/foo/`	Yes	"/my/uri/" matches and "foo" is captured as `label`. The trailing "/" is ignored.
`http://yourhost/my/uri/foo?query=bar`	Yes	"/my/uri/" matches and "foo" is captured as `label`.
`http://yourhost/my/uri/foo#bar`	Yes	"/my/uri/" matches and "foo" is captured as `label`.
`http://yourhost/my/uri/bar`	Yes	"/my/uri/" matches and "bar" is captured as `label`.
`http://yourhost/my/uri`	No	"/my/uri" matches but is missing a segment for `label`.
`http://yourhost/my/uri/foo/bar`	No	Found a trailing segment "/bar".

Any number of labels can be included within a pattern, provided that they are not immediately adjacent and do not have identical label names. Given a pattern of /my/uri/{label1}/{label2} and an endpoint of http://yourhost:

Request URI	Matches?	Reason
`http://yourhost/my/uri/foo/bar`	Yes	Matches literal "/my/uri/", "foo" is captured as `label1`, and "bar" is captured as `label2`.
`http://yourhost/my/uri/bar/baz/`	Yes	Matches literal "/my/uri/", "bar" is captured as `label1`, and "baz" is captured as `label2`.
`http://yourhost/my/uri/foo`	No	Matches literal "/my/uri/" but is missing a segment for `label2`.
`http://yourhost/my/uri`	No	Matches literal "/my/uri/" but is missing segments for `label1` and `label2`.
`http://yourhost/my/uri/foo/bar/baz`	No	Matches literal "/my/uri/", "bar" is captured as `label1`, and "baz" is captured as `label2`, but contains an additional segment "baz".

14.1.2.3. Query string literals#

Components of the query string can be matched literally in the URI pattern. The query string portion of a pattern MUST NOT contain labels.

Literals can be in the form of required keys without values. Given a pattern of /path?requiredKey and an endpoint of http://yourhost:

Request URI	Matches?	Reason
`http://yourhost/path?requiredKey`	Yes	Matches literal "/path" and contains a "requiredKey" query string parameter.
`http://yourhost/path?other&requiredKey`	Yes	Matches literal "/path" and contains a "requiredKey" query string parameter.
`http://yourhost/path`	No	Matches literal "/path" but does not contain the "requiredKey" query string parameter.
`http://yourhost/path?`	No	Matches literal "/path" but does not contain the "requiredKey" query string parameter.
`http://yourhost/path?otherKey`	No	Matches literal "/path" but does not contain the "requiredKey" query string parameter.

Literal query string parameters can be matched with required key-value pairs. Given a pattern of /path?requiredKey=requiredValue and an endpoint of http://yourhost:

Request URI	Matches?	Reason
`http://yourhost/path?requiredKey=requiredValue`	Yes	Matches literal "/path" and contains a query string parameter named "requiredKey" with a value of "requiredValue".
`http://yourhost/path?other&requiredKey=requiredValue`	Yes	Matches literal "/path" and contains a query string parameter named "requiredKey" with a value of "requiredValue". "other" is disregarded or bound to another input member.
`http://yourhost/path`	No	Does not contain a query string parameter named "requiredKey".
`http://yourhost/path?`	No	Does not contain a query string parameter named "requiredKey".
`http://yourhost/path?requiredKey=otherValue`	No	Contains a query string parameter named "requiredKey" but its value is not "requiredValue".

14.1.2.4. Greedy labels#

A greedy label is a label suffixed with the + qualifier that can be used to match more than one path segment. At most, one greedy label may exist in any path pattern, and if present, it SHOULD be the last label in the pattern. Greedy labels MUST be bound to a string shape.

Important

Servers implementing Specificity Routing MAY support more than one greedy label and not require it to be the last label in the pattern. The validation events are therefore emitted as DANGER and can suppressed. Most servers don't support having more than one greedy label. Make sure that your server supports it and test that works as expected before suppressing those events.

Given a pattern of /my/uri/{label+} and an endpoint of http://yourhost:

Request URI	Matches?	Reason
`http://yourhost/my/uri/foo/bar`	Yes	Matches literal "/my/uri/", and "foo/bar" is captured as `label`.
`http://yourhost/my/uri/bar/baz/`	Yes	Matches literal "/my/uri/", and "bar/baz" is captured as `label`.
`http://yourhost/my/uri/foo/bar/baz`	Yes	Matches literal "/my/uri/", and "foo/bar/baz" is captured as `label`.
`http://yourhost/my/uri`	No	Matches literal "/my/uri/" but does not contain a segment to match `label`.

Greedy matching can be used to capture the whole URI to a label, which results in every request for a particular HTTP method being captured. For example, this can be modeled with a pattern of /{label+}.

Segments in the middle of a URI can be captured using greedy labels. Greedy labels match greedily: they will match the longest possible string. Given a pattern of /prefix/{label+}/suffix and an endpoint of https://yourhost:

Request URI	Matches?	Reason
`http://yourhost/prefix/foo/suffix`	Yes	Matches literal "/prefix", captures "foo" in greedy `label`, and matches literal "/suffix".
`http://yourhost/prefix/foo/bar/suffix`	Yes	Matches literal "/prefix", captures "foo/bar" in greedy `label`, and matches literal "/suffix".
`http://yourhost/prefix/foo/bar`	No	Matches literal "/prefix", but does not contain the trailing literal "/suffix".
`http://yourhost/foo/bar/suffix`	No	Does not match the literal "/prefix".
`http://yourhost/prefix/foo/suffix/bar/suffix`	Yes	Matches literal "/prefix", captures "foo/suffix/bar" in greedy `label`, and matches literal "/suffix".
`http://yourhost/prefix/suffix`	No	Matches literal "/prefix", matches literal "/suffix", but does not contain a segment to match `label`.

14.1.2.5. Pattern Validation and Conflict Avoidance#

Smithy validates the patterns within a service against each other to ensure that no two patterns conflict with each other for the same HTTP method. The following rules are in place:

All labels MUST be delimited by '/' characters.
- /{foo}/{bar} is legal
- /{foo}{bar} is illegal
- /{foo}bar/{bar} is illegal
- /{foo}a{bar} is illegal
At most, one greedy label MAY exist per pattern.
- /{foo}/{bar+} is legal
- /{foo+}/bar/{baz+} is illegal
If present, a greedy pattern SHOULD be the last label in a pattern.
- /{foo}/{bar+} is legal
- /{foo+}/bar/{baz} is illegal
Patterns MUST NOT be equivalent if they share a host.
- Pattern /foo/bar and /foo/bar conflict.
- Pattern /foo/{bar} and /foo/{baz} conflict regardless of any constraint traits on the label members.
A label and a literal MAY both occupy the same segment in patterns that are equivalent to that point if they share a host. Server implementations MUST route ambiguous requests to the operation with the most specific URI path (see Specificity Routing.)

14.1.2.6. Specificity Routing#

Specificity routing allows Smithy compliant servers to support ambiguous URI patterns and resolve requests at runtime. The algorithm chooses the best-ranked match using the specificity of the path and literal query parameters when present. The core of the algorithm can be loosely defined as “a path with a non-label segment is considered more specific than one with a label segment in the same position. Similarly a segment with a non-greedy label is considered more specific than a segment with a greedy label segment in the same position.”

The following algorithm is used to compare two paths

Given two ambiguous URI patterns A and B with segments [A0, …, An] and [B0, …, Bm] with query string literals [AQ0, …, AQp] and [BQ0, …, BQq] (with both p and q possibly zero, i.e., without query string literals), the following steps are taken to compare them, for each index x from 0 to min(n, m)

If A[x] and B[x] are both literals then continue (the literal values have to be equal otherwise the patterns are not ambiguous)
If A[x] is a literal and B[x] is a label then A is more specific than B,
If A[x] is a non-greedy label and B[x] is a greedy label then A is more specific than B
If n > m then A is more specific than B
if p > q then A is more specific than B

Routing Example 1

Given a service with the following URI patterns for the same method

/abc/bcd/{xyz}
/abc/{xyz}/cde
/{xyz}/bcd/cde

Request URI	Pattern Matched	Reason
`/abc/bcd/cde`	Pattern 1	Ambiguous with patterns 2 and 3. The literal `bcd` is more specific than the label `{xyz}`
`/abc/foo/cde`	Pattern 2	Ambiguous with pattern 3. The literal segment `abc` is more specific than the label `{xyz}`.
`/foo/bcd/cde`	Pattern 3	Non-ambiguous.

Routing Example 2

Given a service with the following URI patterns for the same method

/abc/bcd/{xyz}
/abc/{xyz}/cde
/{xyz}/bcd/cde?def=efg

Request URI	Pattern Matched	Reason
`/abc/bcd/cde?def=efg`	Pattern 1	Ambiguous with numbers 2 and 3. The literal segment `abc` is more specific than the label `{xyz}`. Notice that path specificity wins over query string literals
`/abc/foo/cde?def=efg`	Pattern 2	Ambiguous with pattern 3. The literal segment `abc` is more specific than the label `{xyz}`.
`/foo/bcd/cde?def=efg`	Pattern 3	Non-ambiguous.

Routing Example 3

Given a service with the following URI patterns for the same method

/abc/{xyz+}/bcd
/abc/{xyz+}

Request URI	Pattern Matched	Reason
`/abc/foo/bar/bcd`	Pattern 1	Ambiguous with numbers 2. The literal segment `bcd` is more specific than a non-segment.
`/abc/foo/bar/baz`	Pattern 2	Non-ambiguous.

14.2. `httpError` trait#

Summary

Defines an HTTP response code for an operation error.

Trait selector

structure[trait|error]

The httpError trait can only be applied to structure shapes that also have the error trait.

Value type

integer value representing the HTTP response status code (for example, 404). The provided value SHOULD be between 400 and 499 for "client" errors or between 500 and 599 for "server" errors.

The following example defines an error with an HTTP status code of 404.

@error("client")
@httpError(404)
structure MyError {}

14.2.1. Default HTTP status codes#

The httpError trait is used to set a custom HTTP response status code. By default, error structures with no httpError trait use the default HTTP status code of the error trait.

400 is used for "client" errors
500 is used for "server" errors

14.3. `httpHeader` trait#

Summary

Binds a structure member to an HTTP header.

Trait selector

structure > :test(member > :test(boolean, number, string, timestamp,
        list > member > :test(boolean, number, string, timestamp)))

The httpHeader trait can be applied to structure members that target a boolean, number, string, or timestamp; or a structure member that targets a list of these types.

Value type

string value defining a valid HTTP header field name according to RFC 9110#section-5.1. The value MUST NOT be empty and MUST be case-insensitively unique across all other members of the structure.

Conflicts with

httpLabel trait, httpQuery trait, httpQueryParams trait, httpPrefixHeaders trait, httpPayload trait, httpResponseCode trait

14.3.1. Serialization rules#

When a list shape is targeted, each member of the shape is serialized as a separate HTTP header either by concatenating the values with a comma on a single line or by serializing each header value on its own line.
boolean values are serialized as true or false.
string values with a mediaType trait are always base64 encoded.
timestamp values are serialized using the http-date format by default, as defined in the IMF-fixdate production of RFC 9110#section-5.6.7. The timestampFormat trait MAY be used to use a custom serialization format.

Note

While there is no limit placed on the length of an HTTP header field, many HTTP client and server implementations enforce limits in practice. Carefully consider the maximum allowed length of each member that is bound to an HTTP header.

Note

httpHeader is only considered when applied to top-level members of an operation's input, output, or error structures. This trait has no meaning in any other context and is simply ignored.

14.3.2. Restricted HTTP headers#

Various HTTP headers are highly discouraged for the httpHeader and httpPrefixHeaders traits.

Header	Reason
Authorization	This header should be populated by authentication traits.
Connection	This is controlled at a lower level by the HTTP client or server.
Content-Length	HTTP clients and servers are responsible for providing a Content-Length header.
Expect	This is controlled at a lower level by the HTTP client.
Host	The Host header is controlled by the HTTP client, not the model.
Max-Forwards	This is controlled at a lower level by the HTTP client.
Proxy-Authenticate	This header should be populated by authentication traits.
Server	The Server header is controlled by the HTTP server, not the model.
TE	This is controlled at a lower level by the HTTP client and server.
Trailer	This is controlled at a lower level by the HTTP client and server.
Transfer-Encoding	This is controlled at a lower level by the HTTP client and server.
Upgrade	This is controlled at a lower level by the HTTP server.
User-Agent	Setting a User-Agent is the responsibility of an HTTP client.
WWW-Authenticate	This header should be populated by authentication traits.
X-Forwarded-For	X-Forwarded-For is an implementation detail of HTTP that does not need to be modeled.

14.4. `httpLabel` trait#

Summary

Binds an operation input structure member to an HTTP label so that it is used as part of an HTTP request URI.

Trait selector

structure > member[trait|required] :test(> :test(string, number, boolean, timestamp))

The httpLabel trait can be applied to structure members marked with the required trait that target a string, number, boolean, or timestamp.

Value type

Annotation trait.

Conflicts with

httpHeader trait, httpQuery trait, httpQueryParams trait, httpPrefixHeaders trait, httpPayload trait, httpResponseCode trait

The following example defines an operation that send an HTTP label named foo as part of the URI of an HTTP request:

$version: "2"
namespace smithy.example

@readonly
@http(method: "GET", uri: "/{foo}")
operation GetStatus {
    input: GetStatusInput
    output: GetStatusOutput
}

@input
structure GetStatusInput {
    @required
    @httpLabel
    foo: String
}

14.4.1. Relationship to http trait #

When a structure is used as the input of an operation, any member of the structure with the httpLabel trait MUST have a corresponding URI label with the same name as the member. httpLabel traits are ignored when serializing operation output or errors.

14.4.2. Applying the `httpLabel` trait to members#

httpLabel can only be applied to structure members that are marked as required.
If the corresponding URI label in the operation is not greedy, then the httpLabel trait MUST target a member that targets a string, byte, short, integer, long, float, double, bigDecimal, bigInteger, boolean, or timestamp.
If the corresponding URI label in the operation is greedy, then the httpLabel trait MUST target a member that targets a string shape.

14.4.3. Serialization rules#

boolean values are serialized as true or false.
timestamp values are serialized as an RFC 3339 string by default (for example, 1985-04-12T23:20:50.52Z, and with percent-encoding, 1985-04-12T23%3A20%3A50.52Z). The timestampFormat trait MAY be used to use a custom serialization format.
Characters not defined as unreserved by RFC 3986 section 2.3 MUST be percent-encoded. That is, all characters except for alphanumerics and -._~.
However, if the label is greedy, then "/" MUST NOT be percent-encoded because greedy labels are meant to span multiple path segments.

14.4.4. `httpLabel` is only used on top-level input#

httpLabel is only considered when applied to top-level members of an operation's input structure. This trait has no meaning in any other context and is simply ignored.

14.5. `httpPayload` trait#

Summary

Binds a single structure member to the body of an HTTP message.

Trait selector

structure > member

Any structure member

Value type

Annotation trait.

Conflicts with

httpLabel trait, httpQuery trait, httpQueryParams trait, httpHeader trait, httpPrefixHeaders trait, httpResponseCode trait

Structurally exclusive

Only a single structure member can be bound to httpPayload.

The following example defines an operation that returns a blob of binary data in a response:

$version: "2"
namespace smithy.example

@readonly
@http(method: "GET", uri: "/random-binary-data")
operation GetRandomBinaryData {
    input: GetRandomBinaryDataInput
    output: GetRandomBinaryDataOutput
}

@input
structure GetRandomBinaryDataInput {}

@output
structure GetRandomBinaryDataOutput {
    @required
    @httpHeader("Content-Type")
    contentType: String

    @httpPayload
    content: Blob
}

14.5.1. Protocol-specific document payloads#

By default, all structure members that are not bound as part of the HTTP message are serialized in a protocol-specific document sent in the body of the message (e.g., a JSON object). The httpPayload trait can be used to bind a single top-level operation input, output, or error structure member to the body of the HTTP message. Multiple members of the same structure MUST NOT be bound to httpPayload.

14.5.2. Binding members to `httpPayload`#

If the httpPayload trait is present on the structure referenced by the input of an operation, then all other structure members MUST be bound with the httpLabel trait, httpHeader trait, httpPrefixHeaders trait, httpQueryParams trait, or httpQuery trait.

If the httpPayload trait is present on the structure referenced by the output of an operation or a structure targeted by the error trait, then all other structure members MUST be bound to a httpHeader trait or httpPrefixHeaders trait.

14.5.3. Serialization rules#

When a string or blob member is referenced, the raw value is serialized as the body of the message.
When any other type of member is referenced, the shape value is serialized as a protocol-specific value that is sent as the body of the message.

Note

httpPayload is only considered when applied to top-level members of an operation's input, output, or error structures. This trait has no meaning in any other context and is simply ignored.

14.6. `httpPrefixHeaders` trait#

Summary

Binds a map of key-value pairs to prefixed HTTP headers.

Trait selector

structure > member
:test(> map :not([trait|sparse]) > member[id|member=value] > string)

The httpPrefixHeaders trait can be applied to structure members that target a map of string. The targeted map MUST NOT be marked with the sparse trait.

Value type

string value that defines the prefix to prepend to each header field name stored in the targeted map member. For example, given a prefix value of "X-Amz-Meta-" and a map key entry of "Baz", the resulting header field name serialized in the message is "X-Amz-Meta-Baz".

Conflicts with

httpLabel trait, httpQuery trait, httpQueryParams trait, httpHeader trait, httpPayload trait, httpResponseCode trait

Structurally exclusive

Only a single structure member can be bound to httpPrefixHeaders.

Given the following Smithy model:

@readonly
@http(method: "GET", uri: "/myOperation")
operation MyOperation {
    input: MyOperationInput
}

@input
structure MyOperationInput {
    @httpPrefixHeaders("X-Foo-")
    headers: StringMap
}

map StringMap {
    key: String
    value: String
}

And given the following input to MyOperation:

{
    "headers": {
        "first": "hi",
        "second": "there"
    }
}

An example HTTP request would be serialized as:

GET /myOperation
Host: <server>
X-Foo-first: hi
X-Foo-second: there

Given the following Smithy model that also uses the httpHeader trait:

@readonly
@http(method: "GET", uri: "/myOperation")
operation MyOperation {
    input: MyOperationInput
}

@input
structure MyOperationInput {
    @httpPrefixHeaders("X-Foo-")
    headers: MapOfStrings

    @httpHeader("X-Foo-Value")
    foo: String
}

map MapOfStrings {
    key: String
    value: String
}

And given the following input to MyOperation:

{
    "headers": {
        "Value": "not sent"
    }
    "foo": "resolved"
}

An example HTTP request would be serialized as:

GET /myOperation
Host: <server>
X-Foo-Value: resolved

14.6.1. Disambiguation of `httpPrefixHeaders`#

In order to differentiate httpPrefixHeaders from other headers, when httpPrefixHeaders are used with a non-empty string, no other httpHeader trait bindings can start with the same prefix provided in httpPrefixHeaders trait.

If httpPrefixHeaders is set to an empty string, then other members can be bound to headers. However, this can lead to ambiguity on the source of provided header values.

Note

httpPrefixHeaders is only considered when applied to top-level members of an operation's input, output, or error structures. This trait has no meaning in any other context and is simply ignored.

14.7. `httpQuery` trait#

Summary

Binds an operation input structure member to a query string parameter.

Trait selector

structure > member
:test(> :test(string, number, boolean, timestamp),
      > list > member > :test(string, number, boolean, timestamp))

The httpQuery trait can be applied to structure members that target a string, number, boolean, or timestamp; or a list of these types.

Value type

A non-empty string value that defines the name of the query string parameter. The query string parameter name MUST be case-sensitively unique across all other members marked with the httpQuery trait.

Conflicts with

httpLabel trait, httpHeader trait, httpQueryParams trait, httpPrefixHeaders trait, httpPayload trait, httpResponseCode trait

The following example defines an operation that optionally sends the color, shape, and size query string parameters in an HTTP request:

@readonly
@http(method: "GET", uri: "/things")
operation ListThings {
    input: ListThingsInput
    output: ListThingsOutput, // omitted for brevity
}

@input
structure ListThingsInput {
    @httpQuery("color")
    color: String

    @httpQuery("shape")
    shape: String

    @httpQuery("size")
    size: Integer
}

14.7.1. Serialization rules#

"&" is used to separate query string parameter key-value pairs.
"=" is used to separate query string parameter names from values.
Characters not defined as unreserved by RFC 3986 section 2.3 MUST be percent-encoded. That is, all characters except for alphanumerics and -._~.
boolean values are serialized as true or false.
timestamp values are serialized as an RFC 3339 date-time string by default (for example, 1985-04-12T23:20:50.52Z, and with percent-encoding, 1985-04-12T23%3A20%3A50.52Z). The timestampFormat trait MAY be used to use a custom serialization format.
List members are serialized by adding multiple query string parameters to the query string using the same name. For example, given a member bound to foo that targets a list of strings with a value of ["a", "b"], the value is serialized in the query string as foo=a&foo=b.
When deserializing, server implementations SHOULD use the first encountered value in the query string for non-list members. For example, given a member bound to foo that targets a string and a query string of foo=a&foo=b, the deserialized value of foo should be a.

Important

Percent-encoding is an implementation detail

The encoding and serialization rules of shapes defined in a Smithy model are implementation details. When designing clients, servers, and other kinds of software based on Smithy models, the format in which the value of a member is serialized SHOULD NOT be a concern of the end-user. As such, members bound to the query string MUST be automatically percent-encoded when serializing HTTP requests and automatically percent-decoded when deserializing HTTP requests.

14.7.2. `httpQuery` is only used on top-level input#

httpQuery is only considered when applied to top-level members of an operation's input structure. This trait has no meaning in any other context and is simply ignored.

Note

While there is no limit placed on the length of an HTTP request line, many HTTP client and server implementations enforce limits in practice. Carefully consider the maximum allowed length of each member that is bound to an HTTP query string or path.

14.8. `httpQueryParams` trait#

Summary

Binds a map of key-value pairs to query string parameters.

Trait selector

structure > member
:test(> map > member[id|member=value] > :test(string, list > member > string))

The httpQueryParams trait can be applied to structure members that target a map of string, or a map of list of string.

Value type

Annotation trait.

Conflicts with

httpLabel trait, httpHeader trait, httpQuery trait, httpPrefixHeaders trait, httpPayload trait, httpResponseCode trait

Structurally exclusive

Only a single structure member can be bound to httpQueryParams.

The following example defines an operation that optionally sends the target input map as query string parameters in an HTTP request:

@readonly
@http(method: "GET", uri: "/things")
operation ListThings {
    input: ListThingsInput
    output: ListThingsOutput, // omitted for brevity
}

@input
structure ListThingsInput {
    @httpQueryParams
    myParams: MapOfStrings
}

map MapOfStrings {
    key: String
    value: String
}

Given the following Smithy model that also uses the httpQuery trait:

@readonly
@http(method: "GET", uri: "/myOperation")
operation MyOperation {
    input: MyOperationInput
}

@input
structure MyOperationInput {
    @httpQueryParams
    query: MapOfStrings

    @httpQuery
    foo: String
}

map MapOfStrings {
    key: String
    value: String
}

And given the following input to MyOperation:

{
    "query": {
        "foo": "not sent"
    }
    "foo": "resolved"
}

An example HTTP request would be serialized as:

GET /myOperation?foo=resolved
Host: <server>

14.8.1. Serialization rules#

See the httpQuery trait serialization rules that define how the keys and values of the target map will be serialized in the request query string. Key-value pairs in the target map are treated like they were explicitly bound using the httpQuery trait, including the requirement that reserved characters MUST be percent-encoded.

When servers deserialize the query string into a map of string, they SHOULD take the first encountered value for each key. Since this rule applies to all future query string values, and changing from a map of string to a map of list of string is backwards-incompatible, care should be taken to use map of string only when it is certain that multiple values for any query string will never be meaningful for the operation.

If a member with the httpQueryParams trait and a member with the httpQuery trait conflict, clients MUST use the value set by the member with the httpQuery trait and disregard the value set by httpQueryParams. For example, given the following model:

@http(method: "POST", uri: "/things")
operation PutThing {
    input: PutThingInput
}

@input
structure PutThingInput {
    @httpQuery
    @required
    thingId: String,

    @httpQueryParams
    tags: MapOfStrings
}

map MapOfStrings {
    key: String
    value: String
}

And given the following input to PutThing:

{
    "thingId": "realId",
    "tags": {
        "thingId": "fakeId",
        "otherTag": "value"
    }
}

An example HTTP request would be serialized as:

POST /things?thingId=realId&otherTag=value
Host: <server>

When deserializing HTTP request query string parameters into members with the httpQueryParams trait, servers MUST treat all values as strings and produce empty string values for keys which do not have values specified. For example, given the following model:

@http(method: "POST", uri: "/things")
operation PostThing {
    input: PostThingInput
}

structure PostThingInput {
    @httpQueryParams
    tags: MapOfStrings
}

map MapOfStrings {
    key: String
    value: String
}

And the following HTTP request:

POST /things?thingId=realId&otherTag=true&anotherTag&lastTag=

A server should deserialize the following input structure:

{
    "tags": {
        "thingId": "realId",
        "otherTag": "true",
        "anotherTag": "",
        "lastTag": ""
    }
}

14.8.2. `httpQueryParams` is only used on top-level input#

httpQueryParams is only considered when applied to top-level members of an operation's input structure. This trait has no meaning in any other context and is simply ignored.

14.9. `httpResponseCode` trait#

Summary

Binds a structure member to the HTTP response status code so that an HTTP response status code can be set dynamically at runtime to something other than code of the http trait.

Trait selector

structure :not([trait|input]) > member :test(> integer)

The httpResponseCode trait can be applied to structure members that target an integer within any structure that has no input trait applied.

Value type

Annotation trait.

Conflicts with

httpLabel trait, httpHeader trait, httpPrefixHeaders trait, httpPayload trait, httpQuery trait, httpQueryParams trait,

14.9.1. `httpResponseCode` use cases#

Marking an output structure member with this trait can be used to provide different response codes for an operation, like a 200 or 201 for a PUT operation. The value for this member SHOULD be between 200 and 299, inclusive. If this member isn't provided, server implementations MUST default to the code set by the http trait.

14.9.2. `httpResponseCode` is only used on top-level output#

httpResponseCode is only considered when applied to top-level members of an operation's output structure. This trait has no meaning in any other context and is simply ignored.

14.10. `cors` trait#

Summary: Defines how a service supports cross-origin resource sharing
Trait selector: service
Value type: structure

The cors trait is a structure that supports the following members:

Property	Type	Description
origin	`string`	The origin from which browser script-originating requests will be allowed. Defaults to `*`.
maxAge	`integer`	The maximum number of seconds for which browsers are allowed to cache the results of a preflight `OPTIONS` request. Defaults to `600`, the maximum age permitted by several browsers. Set to `-1` to disable caching entirely.
additionalAllowedHeaders	`list<string>`	The names of headers that should be included in the `Access-Control-Allow-Headers` header in responses to preflight `OPTIONS` requests. This list will be used in addition to the names of all request headers bound to an input data member via the httpHeader trait, as well as any headers required by the protocol or authentication scheme.
additionalExposedHeaders	`list<string>`	The names of headers that should be included in the `Access-Control-Expose-Headers` header in all responses sent by the service. This list will be used in addition to the names of all request headers bound to an output data member via the httpHeader trait, as well as any headers required by the protocol or authentication scheme.

Adding a cors trait with its value set to an empty object enables cross-origin resource sharing for all origins and allows browser scripts access to all headers to which data is bound in the model, as well as any headers used by the protocol and authentication scheme.

The default settings are not compatible with certain authentication schemes (e.g., http-basic) that rely on browser-managed credentials. Services using such authentication schemes MUST designate a single origin from which cross-origin, credentialed requests will be accepted.

14.11. `httpChecksumRequired` trait#

Summary: Indicates that an operation requires a checksum in its HTTP request. By default, the checksum used for a service is a MD5 checksum passed in the Content-MD5 header.
Trait selector: operation
Value type: Annotation trait.
See: RFC 1864

@httpChecksumRequired
operation PutSomething {
    input: PutSomethingInput
    output: PutSomethingOutput
}

14.12. Serializing HTTP messages#

The following steps are taken to serialize an HTTP request given a map of parameters:

Set the HTTP method to the method property of the http trait of the operation.
Set the URI of the HTTP request to the uri property of the http trait.
Iterate over all of the key-value pairs of the parameters and find the corresponding structure member by name:
1. If the member has the httpLabel trait, expand the value into the URI.
2. If the member has the httpQueryParams trait, serialize the values into the HTTP request as query string parameters.
3. If the member has the httpQuery trait, serialize the value into the HTTP request as a query string parameter.
4. If the member has the httpPrefixHeaders trait and the value is a map, serialize the map key value pairs as prefixed HTTP headers.
5. If the member has the httpHeader trait, serialize the value in an HTTP header using the value of the httpHeader trait.
6. If the member has the httpPayload trait, serialize the value as the body of the request.
7. If the member has no bindings, serialize the key-value pair as part of a protocol-specific document sent in the body of the request.

The following steps are taken to serialize an HTTP response given a map of parameters:

If serializing the output of an operation, set the status code of the response to the code property of the http trait.
If serializing an error and the httpError trait is present, set the status code of the response to its value. Otherwise, set the status code to 400 if the error trait is "client" or to 500 if the error trait is "server".
Iterate over all of the key-value pairs of the parameters and find the corresponding structure member by name:
1. If the member has the httpPrefixHeaders trait and the value is a map, serialize the map key value pairs as prefixed HTTP headers.
2. If the member has the httpHeader trait, serialize the value in an HTTP header using the value of the httpHeader trait.
3. If the member has the httpPayload trait, serialize the value as the body of the response.
4. If the member has no bindings, serialize the key-value pair as part of a protocol-specific document sent in the body of the response.

14.13. Event streams#

When using event streams and HTTP bindings, the httpPayload trait MUST be applied to any input or output member that targets a shape marked with the streaming trait.

The following example defines an operation that uses an input event stream and HTTP bindings:

$version: "2"
namespace smithy.example

@http(method: "POST", uri: "/messages")
operation PublishMessages {
    input: PublishMessagesInput
}

@input
structure PublishMessagesInput {
    @httpPayload
    messages: MessageStream
}

@streaming
union MessageStream {
    message: Message
}

structure Message {
    message: String
}

The following is invalid because the operation has the http trait and an input member is marked with the streaming trait but not marked with the httpPayload trait:

$version: "2"
namespace smithy.example

@http(method: "POST", uri: "/messages")
operation InvalidOperation {
    input: InvalidOperationInput
}

@input
structure InvalidOperationInput {
    invalid: MessageStream  // <-- Missing the @httpPayload trait
}

@streaming
union MessageStream {
    message: Message
}

structure Message {
    message: String
}

14. HTTP bindings#

14.1. http trait#

14.1.1. method#

14.1.2. uri#

14.1.2.1. Literal character sequences#

14.1.2.2. Labels#

14.1.2.3. Query string literals#

14.1.2.4. Greedy labels#

14.1.2.5. Pattern Validation and Conflict Avoidance#

14.1.2.6. Specificity Routing#

14.2. httpError trait#

14.2.1. Default HTTP status codes#

14.3. httpHeader trait#

14.3.1. Serialization rules#

14.3.2. Restricted HTTP headers#

14.4. httpLabel trait#

14.4.1. Relationship to http trait#

14.4.2. Applying the httpLabel trait to members#

14.4.3. Serialization rules#

14.4.4. httpLabel is only used on top-level input#

14.5. httpPayload trait#

14.5.1. Protocol-specific document payloads#

14.5.2. Binding members to httpPayload#

14.5.3. Serialization rules#

14.6. httpPrefixHeaders trait#

14.6.1. Disambiguation of httpPrefixHeaders#

14.7. httpQuery trait#

14.7.1. Serialization rules#

14.7.2. httpQuery is only used on top-level input#

14.8. httpQueryParams trait#

14.8.1. Serialization rules#

14.8.2. httpQueryParams is only used on top-level input#

14.9. httpResponseCode trait#

14.9.1. httpResponseCode use cases#

14.9.2. httpResponseCode is only used on top-level output#

14.10. cors trait#

14.11. httpChecksumRequired trait#

14.12. Serializing HTTP messages#

14.13. Event streams#

14.1. `http` trait#

14.2. `httpError` trait#

14.3. `httpHeader` trait#

14.4. `httpLabel` trait#

14.4.1. Relationship to http trait #

14.4.2. Applying the `httpLabel` trait to members#

14.4.4. `httpLabel` is only used on top-level input#

14.5. `httpPayload` trait#

14.5.2. Binding members to `httpPayload`#

14.6. `httpPrefixHeaders` trait#

14.6.1. Disambiguation of `httpPrefixHeaders`#

14.7. `httpQuery` trait#

14.7.2. `httpQuery` is only used on top-level input#

14.8. `httpQueryParams` trait#

14.8.2. `httpQueryParams` is only used on top-level input#

14.9. `httpResponseCode` trait#

14.9.1. `httpResponseCode` use cases#

14.9.2. `httpResponseCode` is only used on top-level output#

14.10. `cors` trait#

14.11. `httpChecksumRequired` trait#