path: root/doc/src/guide/req.ezdoc
diff options
authorLoïc Hoguin <[email protected]>2014-09-23 16:43:29 +0300
committerLoïc Hoguin <[email protected]>2014-09-23 16:43:29 +0300
commitf1c3b6d76f0c97e1ab927c288bb94891ae4c253b (patch)
tree5a14c007cdcb487032162b3ca96df648f521321a /doc/src/guide/req.ezdoc
parentb57f94661f5fd186f55eb0fead49849e0b1399d1 (diff)
Breaking update of the cowboy_req interface
Simplify the interface for most cowboy_req functions. They all return a single value except the four body reading functions. The reply functions now only return a Req value. Access functions do not return a Req anymore. Functions that used to cache results do not have a cache anymore. The interface for accessing query string and cookies has therefore been changed. There are now three query string functions: qs/1 provides access to the raw query string value; parse_qs/1 returns the query string as a list of key/values; match_qs/2 returns a map containing the values requested in the second argument, after applying constraints and default value. Similarly, there are two cookie functions: parse_cookies/1 and match_cookies/2. More match functions will be added in future commits. None of the functions return an error tuple anymore. It either works or crashes. Cowboy will attempt to provide an appropriate status code in the response of crashed handlers. As a result, the content decode function has its return value changed to a simple binary, and the body reading functions only return on success.
Diffstat (limited to 'doc/src/guide/req.ezdoc')
1 files changed, 69 insertions, 87 deletions
diff --git a/doc/src/guide/req.ezdoc b/doc/src/guide/req.ezdoc
index 9501158..1349af3 100644
--- a/doc/src/guide/req.ezdoc
+++ b/doc/src/guide/req.ezdoc
@@ -27,47 +27,22 @@ For example, when streaming the request body, the
function will return the body by chunks, one at a
time, until there is none left.
-It also caches the result of operations performed
-on the immutable state. That means that some calls
-will give a result much faster when called many times.
:: Overview of the cowboy_req interface
-The `cowboy_req` interface is divided in four groups
-of functions, each having a well defined return type
-signature common to the entire group.
-The first group, access functions, will always return
-`{Value, Req}`. The group includes all the following
-functions: `binding/{2,3}`, `bindings/1`, `body_length/1`,
-`cookie/{2,3}`, `cookies/1`, `header/{2,3}`, `headers/1`,
-`host/1`, `host_info/1`, `host_url/1`, `meta/{2,3}`,
-`method/1`, `path/1`, `path_info/1`, `peer/1`, `port/1`,
-`qs/1`, `qs_val/{2,3}`, `qs_vals/1`, `url/1`, `version/1`.
-The second group, question functions, will always return
-a `boolean()`. The group includes the following three
-functions: `has_body/1`, `has_resp_body/1`, `has_resp_header/2`.
-The third group contains the functions that manipulate
-the socket or perform operations that may legitimately fail.
-They may return `{Result, Req}`, `{Result, Value, Req}`
-or `{error, atom()}`. This includes the following functions:
-`body/{1,2}`, `body_qs/{1,2}`, `chunked_reply/{2,3}`,
-`parse_header/{2,3}`, `part/{1,2}`, `part_body/{1,2}`
-and `reply/{2,3,4}`. Finally, the group also includes the
-`chunk/2` and `continue/1` functions which always return `ok`.
-The final group modifies the Req object state without
-performing any immediate operations. As these functions
-can't fail, they always return a new `Req` directly.
-This includes the following functions: `compact/1`,
-`delete_resp_header/2`, `set_meta/3`, `set_resp_body/2`,
-`set_resp_body_fun/{2,3}`, `set_resp_cookie/4`, `set_resp_header/3`.
-This chapter covers most of the first group, plus a few other
-functions. The next few chapters cover cookies handling, reading
-the request body and sending a response.
+With the exception of functions manipulating the request
+body, all functions return a single value. Depending on
+the function this can be the requested value (method,
+host, path, ...), a boolean (has_body, has_resp_header...)
+a new Req object (set_resp_body, set_resp_header...), or
+simply the atom `ok` (chunk, continue, ...).
+The request body reading functions may return `{Result, Req}`
+or `{Result, Value, Req}`. The functions in this category
+are `body/{1,2}`, `body_qs/{1,2}`, `part/{1,2}`, `part_body/{1,2}`.
+This chapter covers the access functions mainly. Cookies,
+request body and response functions are covered in their
+own chapters.
:: Request
@@ -82,7 +57,7 @@ GET, HEAD, OPTIONS, PATCH, POST, PUT, DELETE. Method names
are case sensitive.
``` erlang
-{Method, Req2} = cowboy_req:method(Req).
+Method = cowboy_req:method(Req).
The host, port and path parts of the URL identify the resource
@@ -90,15 +65,15 @@ being accessed. The host and port information may not be
available if the client uses HTTP/1.0.
``` erlang
-{Host, Req2} = cowboy_req:host(Req),
-{Port, Req3} = cowboy_req:port(Req2),
-{Path, Req4} = cowboy_req:path(Req3).
+Host = cowboy_req:host(Req),
+Port = cowboy_req:port(Req),
+Path = cowboy_req:path(Req).
The version used by the client can of course also be obtained.
``` erlang
-{Version, Req2} = cowboy_req:version(Req).
+Version = cowboy_req:version(Req).
Do note however that clients claiming to implement one version
@@ -115,21 +90,21 @@ You can fetch a single binding. The value will be `undefined`
if the binding doesn't exist.
``` erlang
-{Binding, Req2} = cowboy_req:binding(my_binding, Req).
+Binding = cowboy_req:binding(my_binding, Req).
If you need a different value when the binding doesn't exist,
you can change the default.
``` erlang
-{Binding, Req2} = cowboy_req:binding(my_binding, Req, 42).
+Binding = cowboy_req:binding(my_binding, Req, 42).
You can also obtain all bindings in one call. They will be
returned as a list of key/value tuples.
``` erlang
-{AllBindings, Req2} = cowboy_req:bindings(Req).
+AllBindings = cowboy_req:bindings(Req).
If you used `...` at the beginning of the route's pattern
@@ -137,7 +112,7 @@ for the host, you can retrieve the matched part of the host.
The value will be `undefined` otherwise.
``` erlang
-{HostInfo, Req2} = cowboy_req:host_info(Req).
+HostInfo = cowboy_req:host_info(Req).
Similarly, if you used `...` at the end of the route's
@@ -145,49 +120,70 @@ pattern for the path, you can retrieve the matched part,
or get `undefined` otherwise.
``` erlang
-{PathInfo, Req2} = cowboy_req:path_info(Req).
+PathInfo = cowboy_req:path_info(Req).
:: Query string
-The query string can be obtained directly.
+The raw query string can be obtained directly.
+``` erlang
+Qs = cowboy_req:qs(Req).
+You can parse the query string and then use standard library
+functions to access individual values.
``` erlang
-{Qs, Req2} = cowboy_req:qs(Req).
+QsVals = cowboy_req:parse_qs(Req),
+{_, Lang} = lists:keyfind(<<"lang">>, 1, QsVals).
-You can also requests only one value.
+You can match the query string into a map.
``` erlang
-{QsVal, Req2} = cowboy_req:qs_val(<<"lang">>, Req).
+#{id := ID, lang := Lang} = cowboy_req:match_qs(Req, [id, lang]).
-If that value is optional, you can define a default to simplify
-your task.
+You can use constraints to validate the values while matching
+them. The following snippet will crash if the `id` value is
+not an integer number or if the `lang` value is empty. Additionally
+the `id` value will be converted to an integer term, saving
+you a conversion step.
``` erlang
-{QsVal, Req2} = cowboy_req:qs_val(<<"lang">>, Req, <<"en">>).
+QsMap = cowboy_req:match_qs(Req, [{id, int}, {lang, nonempty}]).
-Finally, you can obtain all query string values.
+Note that in the case of duplicate query string keys, the map
+value will become a list of the different values.
+Read more about ^constraints^.
+A default value can be provided. The default will be used
+if the `lang` key is not found. It will not be used if
+the key is found but has an empty value.
``` erlang
-{AllValues, Req2} = cowboy_req:qs_vals(Req).
+#{lang := Lang} = cowboy_req:match_qs(Req, [{lang, [], <<"en-US">>}]).
+If no default is provided and the value is missing, the
+query string is deemed invalid and the process will crash.
:: Request URL
You can reconstruct the full URL of the resource.
``` erlang
-{URL, Req2} = cowboy_req:url(Req).
+URL = cowboy_req:url(Req).
You can also obtain only the base of the URL, excluding the
path and query string.
``` erlang
-{BaseURL, Req2} = cowboy_req:host_url(Req).
+BaseURL = cowboy_req:host_url(Req).
:: Headers
@@ -198,57 +194,43 @@ or parsed into a more meaningful representation.
This will get the string value of a header.
``` erlang
-{HeaderVal, Req2} = cowboy_req:header(<<"content-type">>, Req).
+HeaderVal = cowboy_req:header(<<"content-type">>, Req).
You can of course set a default in case the header is missing.
``` erlang
-{HeaderVal, Req2}
= cowboy_req:header(<<"content-type">>, Req, <<"text/plain">>).
And also obtain all headers.
``` erlang
-{AllHeaders, Req2} = cowboy_req:headers(Req).
+AllHeaders = cowboy_req:headers(Req).
To parse the previous header, simply call `parse_header/{2,3}`
-where you would call `header/{2,3}` otherwise. Note that the
-return value changes and includes the result of the operation
-as the first element of the returned tuple. A successful parse
-returns `ok`.
-``` erlang
-{ok, ParsedVal, Req2} = cowboy_req:parse_header(<<"content-type">>, Req).
-When Cowboy doesn't know how to parse the given header, the
-result of the operation will be `undefined` and the string value
-will be returned instead.
+where you would call `header/{2,3}` otherwise.
``` erlang
-{undefined, HeaderVal, Req2}
- = cowboy_req:parse_header(<<"unicorn-header">>, Req).
+ParsedVal = cowboy_req:parse_header(<<"content-type">>, Req).
-When parsing fails, `{error, Reason}` is returned instead.
+Cowboy will crash if it doesn't know how to parse the given
+header, or if the value is invalid.
You can of course define a default value. Note that the default
value you specify here is the parsed value you'd like to get
by default.
``` erlang
-{ok, ParsedVal, Req2}
- = cowboy_req:parse_header(<<"content-type">>, Req,
- {<<"text">>, <<"plain">>, []}).
+ParsedVal = cowboy_req:parse_header(<<"content-type">>, Req,
+ {<<"text">>, <<"plain">>, []}).
The list of known headers and default values is defined in the
-manual. Also note that the result of parsing is cached, so
-calling this function multiple times for the same values will
-not have a significant performance impact.
:: Meta
@@ -260,13 +242,13 @@ This will get a meta value. The returned value will be `undefined`
if it isn't defined.
``` erlang
-{MetaVal, Req2} = cowboy_req:meta(websocket_version, Req).
+MetaVal = cowboy_req:meta(websocket_version, Req).
You can change the default value if needed.
``` erlang
-{MetaVal, Req2} = cowboy_req:meta(websocket_version, Req, 13).
+MetaVal = cowboy_req:meta(websocket_version, Req, 13).
You can also define your own meta values. The name must be
@@ -283,7 +265,7 @@ not necessarily the actual IP and port of the client, but
rather the one of the machine that connected to the server.
``` erlang
-{{IP, Port}, Req2} = cowboy_req:peer(Req).
+{IP, Port} = cowboy_req:peer(Req).
:: Reducing the memory footprint