func()

in http2/transport.go [1711:1877]

• 127 lines of code
• 40 McCabe index (conditional complexity)

func (cc *ClientConn) encodeHeaders(req *http.Request, addGzipHeader bool, trailers string, contentLength int64) ([]byte, error) {
	cc.hbuf.Reset()
	if req.URL == nil {
		return nil, errNilRequestURL
	}

	host := req.Host
	if host == "" {
		host = req.URL.Host
	}
	host, err := httpguts.PunycodeHostPort(host)
	if err != nil {
		return nil, err
	}

	var path string
	if req.Method != "CONNECT" {
		path = req.URL.RequestURI()
		if !validPseudoPath(path) {
			orig := path
			path = strings.TrimPrefix(path, req.URL.Scheme+"://"+host)
			if !validPseudoPath(path) {
				if req.URL.Opaque != "" {
					return nil, fmt.Errorf("invalid request :path %q from URL.Opaque = %q", orig, req.URL.Opaque)
				} else {
					return nil, fmt.Errorf("invalid request :path %q", orig)
				}
			}
		}
	}

	// Check for any invalid headers and return an error before we
	// potentially pollute our hpack state. (We want to be able to
	// continue to reuse the hpack encoder for future requests)
	for k, vv := range req.Header {
		if !httpguts.ValidHeaderFieldName(k) {
			return nil, fmt.Errorf("invalid HTTP header name %q", k)
		}
		for _, v := range vv {
			if !httpguts.ValidHeaderFieldValue(v) {
				return nil, fmt.Errorf("invalid HTTP header value %q for header %q", v, k)
			}
		}
	}

	enumerateHeaders := func(f func(name, value string)) {
		// 8.1.2.3 Request Pseudo-Header Fields
		// The :path pseudo-header field includes the path and query parts of the
		// target URI (the path-absolute production and optionally a '?' character
		// followed by the query production (see Sections 3.3 and 3.4 of
		// [RFC3986]).
		f(":authority", host)
		m := req.Method
		if m == "" {
			m = http.MethodGet
		}
		f(":method", m)
		if req.Method != "CONNECT" {
			f(":path", path)
			f(":scheme", req.URL.Scheme)
		}
		if trailers != "" {
			f("trailer", trailers)
		}

		var didUA bool
		for k, vv := range req.Header {
			if asciiEqualFold(k, "host") || asciiEqualFold(k, "content-length") {
				// Host is :authority, already sent.
				// Content-Length is automatic, set below.
				continue
			} else if asciiEqualFold(k, "connection") ||
				asciiEqualFold(k, "proxy-connection") ||
				asciiEqualFold(k, "transfer-encoding") ||
				asciiEqualFold(k, "upgrade") ||
				asciiEqualFold(k, "keep-alive") {
				// Per 8.1.2.2 Connection-Specific Header
				// Fields, don't send connection-specific
				// fields. We have already checked if any
				// are error-worthy so just ignore the rest.
				continue
			} else if asciiEqualFold(k, "user-agent") {
				// Match Go's http1 behavior: at most one
				// User-Agent. If set to nil or empty string,
				// then omit it. Otherwise if not mentioned,
				// include the default (below).
				didUA = true
				if len(vv) < 1 {
					continue
				}
				vv = vv[:1]
				if vv[0] == "" {
					continue
				}
			} else if asciiEqualFold(k, "cookie") {
				// Per 8.1.2.5 To allow for better compression efficiency, the
				// Cookie header field MAY be split into separate header fields,
				// each with one or more cookie-pairs.
				for _, v := range vv {
					for {
						p := strings.IndexByte(v, ';')
						if p < 0 {
							break
						}
						f("cookie", v[:p])
						p++
						// strip space after semicolon if any.
						for p+1 <= len(v) && v[p] == ' ' {
							p++
						}
						v = v[p:]
					}
					if len(v) > 0 {
						f("cookie", v)
					}
				}
				continue
			}

			for _, v := range vv {
				f(k, v)
			}
		}
		if shouldSendReqContentLength(req.Method, contentLength) {
			f("content-length", strconv.FormatInt(contentLength, 10))
		}
		if addGzipHeader {
			f("accept-encoding", "gzip")
		}
		if !didUA {
			f("user-agent", defaultUserAgent)
		}
	}

	// Do a first pass over the headers counting bytes to ensure
	// we don't exceed cc.peerMaxHeaderListSize. This is done as a
	// separate pass before encoding the headers to prevent
	// modifying the hpack state.
	hlSize := uint64(0)
	enumerateHeaders(func(name, value string) {
		hf := hpack.HeaderField{Name: name, Value: value}
		hlSize += uint64(hf.Size())
	})

	if hlSize > cc.peerMaxHeaderListSize {
		return nil, errRequestHeaderListSize
	}

	trace := httptrace.ContextClientTrace(req.Context())
	traceHeaders := traceHasWroteHeaderField(trace)

	// Header list size is ok. Write the headers.
	enumerateHeaders(func(name, value string) {
		name, ascii := asciiToLower(name)
		if !ascii {
			// Skip writing invalid headers. Per RFC 7540, Section 8.1.2, header
			// field names have to be ASCII characters (just as in HTTP/1.x).
			return
		}
		cc.writeHeader(name, value)
		if traceHeaders {
			traceWroteHeaderField(trace, name, value)
		}
	})

	return cc.hbuf.Bytes(), nil
}