Implement post overload in std.net.curl

This overload provides the ability to send properly escaped
www-form-urlencoded data using an associative array. The data is built into
name value pairs using an Appender!string that reserves 128 bytes per name
value pair. An example was added to the documentation and the existing one
changed as this is the more common use case.

Several corrections to coding style were suggested and corrected.

std/net/curl.d

@@ -96,11 +96,11 @@ Example:
 ---
 import std.net.curl, std.stdio;
 
-// Return a char[] containing the content specified by an URL
+// Return a char[] containing the content specified by a URL
 auto content = get("dlang.org");
 
-// Post data and return a char[] containing the content specified by an URL
-auto content = post("mydomain.com/here.cgi", "post data");
+// Post data and return a char[] containing the content specified by a URL
+auto content = post("mydomain.com/here.cgi", ["name1" : "value1", "name2" : "value2"]);
 
 // Get content of file from ftp server
 auto content = get("ftp.digitalmars.com/sieve.ds");
@@ -566,22 +566,26 @@ unittest
 /** HTTP post content.
  *
  * Params:
- * url = resource to post to
- * postData = data to send as the body of the request. An array
- *            of an arbitrary type is accepted and will be cast to ubyte[]
- *            before sending it.
- * conn = HTTP connection to use
+ *     url = resource to post to
+ *     postDict = data to send as the body of the request. An associative array
+ *                of $(D string) is accepted and will be encoded using
+ *                www-form-urlencoding
+ *     postData = data to send as the body of the request. An array
+ *                of an arbitrary type is accepted and will be cast to ubyte[]
+ *                before sending it.
+ *     conn = HTTP connection to use
+ *     T    = The template parameter $(D T) specifies the type to return. Possible values
+ *            are $(D char) and $(D ubyte) to return $(D char[]) or $(D ubyte[]). If asking
+ *            for $(D char), content will be converted from the connection character set
+ *            (specified in HTTP response headers or FTP connection properties, both ISO-8859-1
+ *            by default) to UTF-8.
  *
- * The template parameter $(D T) specifies the type to return. Possible values
- * are $(D char) and $(D ubyte) to return $(D char[]) or $(D ubyte[]). If asking
- * for $(D char), content will be converted from the connection character set
- * (specified in HTTP response headers or FTP connection properties, both ISO-8859-1
- * by default) to UTF-8.
- *
- * Example:
+ * Examples:
  * ----
  * import std.net.curl;
- * auto content = post("d-lang.appspot.com/testUrl2", [1,2,3,4]);
+ *
+ * auto content1 = post("d-lang.appspot.com/testUrl2", ["name1" : "value1", "name2" : "value2"]);
+ * auto content2 = post("d-lang.appspot.com/testUrl2", [1,2,3,4]);
  * ----
  *
  * Returns:
@@ -627,6 +631,27 @@ unittest
     assert(res == cast(ubyte[])[17, 27, 35, 41]);
 }
 
+/// ditto
+T[] post(T = char)(const(char)[] url, string[string] postDict, HTTP conn = HTTP())
+if (is(T == char) || is(T == ubyte))
+{
+    import std.uri : urlEncode;
+
+    return post(url, urlEncode(postDict), conn);
+}
+
+unittest
+{
+    foreach (host; [testServer.addr, "http://" ~ testServer.addr])
+    {
+        testServer.handle((s) {
+            auto req = s.recvReq!char;
+            s.send(httpOK(req.bdy));
+        });
+        auto res = post(host ~ "/path", ["name1" : "value1", "name2" : "value2"]);
+        assert(res == "name1=value1&name2=value2");
+    }
+}
 
 /** HTTP/FTP put content.
  *

std/uri.d

@@ -372,6 +372,44 @@ string encodeComponent(Char)(in Char[] uriComponent) if (isSomeChar!Char)
     return URI_Encode(s, URI_Alpha | URI_Digit | URI_Mark);
 }
 
+/* Encode associative array using www-form-urlencoding
+ *
+ * Params:
+ *      values = an associative array containing the values to be encoded.
+ *
+ * Returns:
+ *      A string encoded using www-form-urlencoding.
+ */
+package string urlEncode(in string[string] values)
+{
+    if (values.length == 0)
+        return "";
+
+    import std.array : Appender;
+    import std.format : formattedWrite;
+
+    Appender!string enc;
+    enc.reserve(values.length * 128);
+
+    bool first = true;
+    foreach (k, v; values)
+    {
+        if (!first)
+            enc.put('&');
+        formattedWrite(enc, "%s=%s", encodeComponent(k), encodeComponent(v));
+        first = false;
+    }
+    return enc.data;
+}
+
+unittest
+{
+    string[string] a;
+    assert(urlEncode(a) == "");
+    assert(urlEncode(["name1" : "value1"]) == "name1=value1");
+    assert(urlEncode(["name1" : "value1", "name2" : "value2"]) == "name1=value1&name2=value2");
+}
+
 /***************************
  * Does string s[] start with a URL?
  * Returns: