[confighttp] Add omitempty tag to fields (#12482)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

Depends on
#12481.

Note that I didn't add the tag to any fields where we set a default
value. This is because the zero value is significant in these cases and
omitting it from the output would cause it to be set to the default
instead of the zero value. We could fix this with a custom interface
implemented by our config structs, but that will have to be a separate
effort, and simply using the `omitempty` tag is still an improvement for
most fields.

<!-- Issue number if applicable -->
#### Link to tracking issue

Works toward
#12191

Author: evan-bradley

.chloggen/confighttp-omitempty.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confighttp
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add the `omitempty` mapstructure tag to struct fields
+
+# One or more tracking issues or pull requests related to the change
+issues: [12191]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: This results in unset fields not being rendered when marshaling.
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [api]

config/confighttp/confighttp.go

@@ -42,51 +42,51 @@ var defaultCompressionAlgorithms = []string{"", "gzip", "zstd", "zlib", "snappy"
 // ClientConfig defines settings for creating an HTTP client.
 type ClientConfig struct {
 	// The target URL to send data to (e.g.: http://some.url:9411/v1/traces).
-	Endpoint string `mapstructure:"endpoint"`
+	Endpoint string `mapstructure:"endpoint,omitempty"`
 
 	// ProxyURL setting for the collector
-	ProxyURL string `mapstructure:"proxy_url"`
+	ProxyURL string `mapstructure:"proxy_url,omitempty"`
 
 	// TLSSetting struct exposes TLS client configuration.
-	TLSSetting configtls.ClientConfig `mapstructure:"tls"`
+	TLSSetting configtls.ClientConfig `mapstructure:"tls,omitempty"`
 
 	// ReadBufferSize for HTTP client. See http.Transport.ReadBufferSize.
 	// Default is 0.
-	ReadBufferSize int `mapstructure:"read_buffer_size"`
+	ReadBufferSize int `mapstructure:"read_buffer_size,omitempty"`
 
 	// WriteBufferSize for HTTP client. See http.Transport.WriteBufferSize.
 	// Default is 0.
-	WriteBufferSize int `mapstructure:"write_buffer_size"`
+	WriteBufferSize int `mapstructure:"write_buffer_size,omitempty"`
 
 	// Timeout parameter configures `http.Client.Timeout`.
 	// Default is 0 (unlimited).
-	Timeout time.Duration `mapstructure:"timeout"`
+	Timeout time.Duration `mapstructure:"timeout,omitempty"`
 
 	// Additional headers attached to each HTTP request sent by the client.
 	// Existing header values are overwritten if collision happens.
 	// Header values are opaque since they may be sensitive.
-	Headers map[string]configopaque.String `mapstructure:"headers"`
+	Headers map[string]configopaque.String `mapstructure:"headers,omitempty"`
 
 	// Auth configuration for outgoing HTTP calls.
-	Auth *configauth.Authentication `mapstructure:"auth"`
+	Auth *configauth.Authentication `mapstructure:"auth,omitempty"`
 
 	// The compression key for supported compression types within collector.
-	Compression configcompression.Type `mapstructure:"compression"`
+	Compression configcompression.Type `mapstructure:"compression,omitempty"`
 
 	// Advanced configuration options for the Compression
-	CompressionParams configcompression.CompressionParams `mapstructure:"compression_params"`
+	CompressionParams configcompression.CompressionParams `mapstructure:"compression_params,omitempty"`
 
 	// MaxIdleConns is used to set a limit to the maximum idle HTTP connections the client can keep open.
 	// By default, it is set to 100. Zero means no limit.
 	MaxIdleConns int `mapstructure:"max_idle_conns"`
 
 	// MaxIdleConnsPerHost is used to set a limit to the maximum idle HTTP connections the host can keep open.
 	// Default is 0 (unlimited).
-	MaxIdleConnsPerHost int `mapstructure:"max_idle_conns_per_host"`
+	MaxIdleConnsPerHost int `mapstructure:"max_idle_conns_per_host,omitempty"`
 
 	// MaxConnsPerHost limits the total number of connections per host, including connections in the dialing,
 	// active, and idle states. Default is 0 (unlimited).
-	MaxConnsPerHost int `mapstructure:"max_conns_per_host"`
+	MaxConnsPerHost int `mapstructure:"max_conns_per_host,omitempty"`
 
 	// IdleConnTimeout is the maximum amount of time a connection will remain open before closing itself.
 	// By default, it is set to 90 seconds.
@@ -98,25 +98,25 @@ type ClientConfig struct {
 	// WARNING: enabling this option can result in significant overhead establishing a new HTTP(S)
 	// connection for every request. Before enabling this option please consider whether changes
 	// to idle connection settings can achieve your goal.
-	DisableKeepAlives bool `mapstructure:"disable_keep_alives"`
+	DisableKeepAlives bool `mapstructure:"disable_keep_alives,omitempty"`
 
 	// This is needed in case you run into
 	// https://github.com/golang/go/issues/59690
 	// https://github.com/golang/go/issues/36026
 	// HTTP2ReadIdleTimeout if the connection has been idle for the configured value send a ping frame for health check
 	// 0s means no health check will be performed.
-	HTTP2ReadIdleTimeout time.Duration `mapstructure:"http2_read_idle_timeout"`
+	HTTP2ReadIdleTimeout time.Duration `mapstructure:"http2_read_idle_timeout,omitempty"`
 	// HTTP2PingTimeout if there's no response to the ping within the configured value, the connection will be closed.
 	// If not set or set to 0, it defaults to 15s.
-	HTTP2PingTimeout time.Duration `mapstructure:"http2_ping_timeout"`
+	HTTP2PingTimeout time.Duration `mapstructure:"http2_ping_timeout,omitempty"`
 	// Cookies configures the cookie management of the HTTP client.
-	Cookies *CookiesConfig `mapstructure:"cookies"`
+	Cookies *CookiesConfig `mapstructure:"cookies,omitempty"`
 }
 
 // CookiesConfig defines the configuration of the HTTP client regarding cookies served by the server.
 type CookiesConfig struct {
 	// Enabled if true, cookies from HTTP responses will be reused in further HTTP requests with the same server.
-	Enabled bool `mapstructure:"enabled"`
+	Enabled bool `mapstructure:"enabled,omitempty"`
 }
 
 // NewDefaultClientConfig returns ClientConfig type object with
@@ -284,7 +284,7 @@ func (interceptor *headerRoundTripper) RoundTrip(req *http.Request) (*http.Respo
 // ServerConfig defines settings for creating an HTTP server.
 type ServerConfig struct {
 	// Endpoint configures the listening address for the server.
-	Endpoint string `mapstructure:"endpoint"`
+	Endpoint string `mapstructure:"endpoint,omitempty"`
 
 	// TLSSetting struct exposes TLS client configuration.
 	TLSSetting *configtls.ServerConfig `mapstructure:"tls"`
@@ -293,20 +293,20 @@ type ServerConfig struct {
 	CORS *CORSConfig `mapstructure:"cors"`
 
 	// Auth for this receiver
-	Auth *AuthConfig `mapstructure:"auth"`
+	Auth *AuthConfig `mapstructure:"auth,omitempty"`
 
 	// MaxRequestBodySize sets the maximum request body size in bytes. Default: 20MiB.
-	MaxRequestBodySize int64 `mapstructure:"max_request_body_size"`
+	MaxRequestBodySize int64 `mapstructure:"max_request_body_size,omitempty"`
 
 	// IncludeMetadata propagates the client metadata from the incoming requests to the downstream consumers
-	IncludeMetadata bool `mapstructure:"include_metadata"`
+	IncludeMetadata bool `mapstructure:"include_metadata,omitempty"`
 
 	// Additional headers attached to each HTTP response sent to the client.
 	// Header values are opaque since they may be sensitive.
 	ResponseHeaders map[string]configopaque.String `mapstructure:"response_headers"`
 
 	// CompressionAlgorithms configures the list of compression algorithms the server can accept. Default: ["", "gzip", "zstd", "zlib", "snappy", "deflate"]
-	CompressionAlgorithms []string `mapstructure:"compression_algorithms"`
+	CompressionAlgorithms []string `mapstructure:"compression_algorithms,omitempty"`
 
 	// ReadTimeout is the maximum duration for reading the entire
 	// request, including the body. A zero or negative value means
@@ -316,7 +316,7 @@ type ServerConfig struct {
 	// decisions on each request body's acceptable deadline or
 	// upload rate, most users will prefer to use
 	// ReadHeaderTimeout. It is valid to use them both.
-	ReadTimeout time.Duration `mapstructure:"read_timeout"`
+	ReadTimeout time.Duration `mapstructure:"read_timeout,omitempty"`
 
 	// ReadHeaderTimeout is the amount of time allowed to read
 	// request headers. The connection's read deadline is reset
@@ -360,7 +360,7 @@ type AuthConfig struct {
 
 	// RequestParameters is a list of parameters that should be extracted from the request and added to the context.
 	// When a parameter is found in both the query string and the header, the value from the query string will be used.
-	RequestParameters []string `mapstructure:"request_params"`
+	RequestParameters []string `mapstructure:"request_params,omitempty"`
 }
 
 // ToListener creates a net.Listener.
@@ -517,19 +517,19 @@ type CORSConfig struct {
 	// HTTP/JSON requests to an OTLP receiver. An origin may contain a
 	// wildcard (*) to replace 0 or more characters (e.g.,
 	// "http://*.domain.com", or "*" to allow any origin).
-	AllowedOrigins []string `mapstructure:"allowed_origins"`
+	AllowedOrigins []string `mapstructure:"allowed_origins,omitempty"`
 
 	// AllowedHeaders sets what headers will be allowed in CORS requests.
 	// The Accept, Accept-Language, Content-Type, and Content-Language
 	// headers are implicitly allowed. If no headers are listed,
 	// X-Requested-With will also be accepted by default. Include "*" to
 	// allow any request header.
-	AllowedHeaders []string `mapstructure:"allowed_headers"`
+	AllowedHeaders []string `mapstructure:"allowed_headers,omitempty"`
 
 	// MaxAge sets the value of the Access-Control-Max-Age response header.
 	// Set it to the number of seconds that browsers should cache a CORS
 	// preflight response for.
-	MaxAge int `mapstructure:"max_age"`
+	MaxAge int `mapstructure:"max_age,omitempty"`
 }
 
 // NewDefaultCORSConfig creates a default cross-origin resource sharing (CORS) configuration.

internal/e2e/confighttp_test.go

@@ -0,0 +1,44 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package e2e
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/collector/config/confighttp"
+	"go.opentelemetry.io/collector/confmap"
+)
+
+func TestConfmapMarshalConfigHTTP(t *testing.T) {
+	conf := confmap.New()
+	require.NoError(t, conf.Marshal(confighttp.NewDefaultClientConfig()))
+	assert.Equal(t, map[string]any{
+		"headers":           map[string]any{},
+		"idle_conn_timeout": 90 * time.Second,
+		"max_idle_conns":    100,
+	}, conf.ToStringMap())
+
+	conf = confmap.New()
+	require.NoError(t, conf.Marshal(confighttp.NewDefaultCORSConfig()))
+	assert.Equal(t, map[string]any{}, conf.ToStringMap())
+
+	conf = confmap.New()
+	require.NoError(t, conf.Marshal(confighttp.NewDefaultServerConfig()))
+	assert.Equal(t, map[string]any{
+		"cors":                map[string]any{},
+		"idle_timeout":        60 * time.Second,
+		"read_header_timeout": 60 * time.Second,
+		"response_headers":    map[string]any{},
+		"tls":                 map[string]any{},
+		"write_timeout":       30 * time.Second,
+	}, conf.ToStringMap())
+
+	conf = confmap.New()
+	require.NoError(t, conf.Marshal(confighttp.AuthConfig{}))
+	assert.Equal(t, map[string]any{}, conf.ToStringMap())
+}