api: Create a new Go module for API; with remote write client and handler.

.bingo/Variables.mk

@@ -1,4 +1,4 @@
-# Auto generated binary variables helper managed by https://github.com/bwplotka/bingo v0.8. DO NOT EDIT.
+# Auto generated binary variables helper managed by https://github.com/bwplotka/bingo v0.9. DO NOT EDIT.
 # All tools are designed to be build inside $GOBIN.
 BINGO_DIR := $(dir $(lastword $(MAKEFILE_LIST)))
 GOPATH ?= $(shell go env GOPATH)
@@ -7,16 +7,22 @@ GO     ?= $(shell which go)
 
 # Below generated variables ensure that every time a tool under each variable is invoked, the correct version
 # will be used; reinstalling only if needed.
-# For example for goimports variable:
+# For example for buf variable:
 #
 # In your main Makefile (for non array binaries):
 #
 #include .bingo/Variables.mk # Assuming -dir was set to .bingo .
 #
-#command: $(GOIMPORTS)
-#	@echo "Running goimports"
-#	@$(GOIMPORTS) <flags/args..>
+#command: $(BUF)
+#	@echo "Running buf"
+#	@$(BUF) <flags/args..>
 #
+BUF := $(GOBIN)/buf-v1.39.0
+$(BUF): $(BINGO_DIR)/buf.mod
+	@# Install binary/ries using Go 1.14+ build command. This is using bwplotka/bingo-controlled, separate go module with pinned dependencies.
+	@echo "(re)installing $(GOBIN)/buf-v1.39.0"
+	@cd $(BINGO_DIR) && GOWORK=off $(GO) build -mod=mod -modfile=buf.mod -o=$(GOBIN)/buf-v1.39.0 "github.com/bufbuild/buf/cmd/buf"
+
 GOIMPORTS := $(GOBIN)/goimports-v0.9.3
 $(GOIMPORTS): $(BINGO_DIR)/goimports.mod
 	@# Install binary/ries using Go 1.14+ build command. This is using bwplotka/bingo-controlled, separate go module with pinned dependencies.

.bingo/buf.mod

@@ -0,0 +1,5 @@
+module _ // Auto generated by https://github.com/bwplotka/bingo. DO NOT EDIT
+
+go 1.22.6
+
+require github.com/bufbuild/buf v1.39.0 // cmd/buf

.bingo/variables.env

@@ -1,4 +1,4 @@
-# Auto generated binary variables helper managed by https://github.com/bwplotka/bingo v0.8. DO NOT EDIT.
+# Auto generated binary variables helper managed by https://github.com/bwplotka/bingo v0.9. DO NOT EDIT.
 # All tools are designed to be build inside $GOBIN.
 # Those variables will work only until 'bingo get' was invoked, or if tools were installed via Makefile's Variables.mk.
 GOBIN=${GOBIN:=$(go env GOBIN)}
@@ -8,5 +8,7 @@ if [ -z "$GOBIN" ]; then
 fi
 
 
+BUF="${GOBIN}/buf-v1.39.0"
+
 GOIMPORTS="${GOBIN}/goimports-v0.9.3"
 

Makefile

@@ -50,3 +50,10 @@ generate-go-collector-test-files:
 .PHONY: fmt
 fmt: common-format
 	$(GOIMPORTS) -local github.com/prometheus/client_golang -w .
+
+RWMODULE = api/remotewrite
+
+.PHONY: proto
+proto: ## Regenerate Go from proto.
+proto: $(BUF)
+	@$(MAKE) -C api/remotewrite proto BUF=$(BUF)

api/remotewrite/Makefile

@@ -0,0 +1,11 @@
+
+.PHONY: proto
+proto: ## Regenerate Go from proto.
+proto: $(BUF)
+	@echo ">> regenerating Prometheus proto"
+	@$(BUF) generate
+	# TODO(bwplotka): Is there a way to configure buf for this?
+	@find genproto/ -type f -exec sed -i '' 's/package prompb/package writev1/g' {} \;
+	# For some reasons buf generates this unused import, kill it manually for now and reformat.
+	@find genproto/ -type f -exec sed -i '' 's/_ "github.com\/gogo\/protobuf\/gogoproto"//g' {} \;
+	@go fmt ./genproto/...

api/remotewrite/buf.gen.yaml

@@ -0,0 +1,26 @@
+# buf.gen.yaml
+version: v2
+
+plugins:
+- remote: buf.build/protocolbuffers/go:v1.31.0
+  out: .
+  opt:
+  - Mio/prometheus/write/v2/types.proto=genproto/v2
+  - Mtypes.proto=genproto/v1
+  - Mremote.proto=genproto/v1
+
+# vtproto for efficiency utilities like pooling etc.
+# https://buf.build/community/planetscale-vtprotobuf?version=v0.6.0
+- remote: buf.build/community/planetscale-vtprotobuf:v0.6.0
+  out: .
+  opt:
+  - Mio/prometheus/write/v2/types.proto=genproto/v2
+  - Mtypes.proto=genproto/v1
+  - Mremote.proto=genproto/v1
+  - features=marshal+unmarshal+size+clone
+
+inputs:
+- module: buf.build/prometheus/prometheus:5b212ab78fb7460e831cf7ff2d83e385
+  types:
+  - "io.prometheus.write.v2.Request"
+  - "prometheus.WriteRequest"

api/remotewrite/client.go

@@ -0,0 +1,266 @@
+// Copyright 2024 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package remotewrite
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/efficientgo/core/backoff"
+	"github.com/klauspost/compress/snappy"
+	writev1 "github.com/prometheus/client_golang/api/remotewrite/genproto/v1"
+	writev2 "github.com/prometheus/client_golang/api/remotewrite/genproto/v2"
+)
+
+const (
+	defaultBackoff = 0
+	maxErrMsgLen   = 1024
+)
+
+type Client struct {
+	logger *slog.Logger
+	url    string
+	client *http.Client
+
+	userAgent        string
+	retryOnRateLimit bool
+
+	compr    Compression
+	comprBuf []byte
+
+	b *backoff.Backoff
+}
+
+type EncodingClient struct {
+	client *Client
+
+	buf []byte
+}
+
+func NewEncodingClient(client *Client) *EncodingClient {
+	return &EncodingClient{client: client}
+}
+
+func (c *EncodingClient) WriteV1(ctx context.Context, req *writev1.WriteRequest, opts *ClientWriteOpts) (WriteResponseStats, error) {
+	size := req.SizeVT()
+	if len(c.buf) < size {
+		c.buf = make([]byte, size)
+	}
+	if _, err := req.MarshalToSizedBufferVT(c.buf[:size]); err != nil {
+		return WriteResponseStats{}, fmt.Errorf("encoding v1 request %w", err)
+	}
+	return c.client.Write(ctx, ProtoMsgV1, c.buf[:size], opts)
+}
+
+func (c *EncodingClient) WriteV2(ctx context.Context, req *writev2.Request, opts *ClientWriteOpts) (WriteResponseStats, error) {
+	size := req.SizeVT()
+	if len(c.buf) < size {
+		c.buf = make([]byte, size)
+	}
+	if _, err := req.MarshalToSizedBufferVT(c.buf[:size]); err != nil {
+		return WriteResponseStats{}, fmt.Errorf("encoding v2 request %w", err)
+	}
+	stats, err := c.client.Write(ctx, ProtoMsgV2, c.buf[:size], opts)
+	if err != nil {
+		return stats, err
+	}
+
+	// Check the case mentioned in PRW 2.0.
+	// https://prometheus.io/docs/specs/remote_write_spec_2_0/#required-written-response-headers.
+	if !stats.Confirmed && stats.NoDataWritten() {
+		cStats := WriteResponseStats{}.AddV2(req)
+		if !cStats.NoDataWritten() {
+			return stats, fmt.Errorf("sent v2 request with %v samples %v histograms %v exemplars; "+
+				"got 2xx, but PRW 2.0 response header statistics indicate %v samples, %v histograms "+
+				"and %v exemplars were accepted; assumining failure e.g. the target only supports "+
+				"PRW 1.0 prometheus.WriteRequest, but does not check the Content-Type header correctly",
+				cStats.Samples, cStats.Histograms, cStats.Exemplars,
+				stats.Samples, stats.Histograms, stats.Exemplars,
+			)
+		}
+	}
+	return stats, nil
+}
+
+// NewClient returns client.
+// TODO(bwplotka): Add variadic options.
+func NewClient(logger *slog.Logger, url string, hc *http.Client, compr Compression, ua string, retryOnRateLimit bool) *Client {
+	if hc == nil {
+		hc = &http.Client{Timeout: 1 * time.Minute}
+	}
+	return &Client{
+		logger:           logger,
+		url:              url,
+		client:           hc,
+		compr:            compr,
+		userAgent:        ua,
+		retryOnRateLimit: retryOnRateLimit,
+	}
+}
+
+type RetryableError struct {
+	error
+	retryAfter time.Duration
+}
+
+func (r RetryableError) RetryAfter() time.Duration {
+	return r.retryAfter
+}
+
+type ClientWriteOpts struct {
+	Backoff backoff.Config
+}
+
+var defaultOpts = &ClientWriteOpts{
+	Backoff: backoff.Config{
+		Min:        1 * time.Second,
+		Max:        10 * time.Second,
+		MaxRetries: 10,
+	},
+}
+
+// TODO(bwplotka): Support variadic options allowing too old sample handling, tracing, metrics
+func (c *Client) Write(ctx context.Context, proto ProtoMsg, serializedRequest []byte, opts *ClientWriteOpts) (WriteResponseStats, error) {
+	o := *defaultOpts
+	if opts != nil {
+		o = *opts
+	}
+	payload, err := compressPayload(&c.comprBuf, c.compr, serializedRequest)
+	if err != nil {
+		return WriteResponseStats{}, fmt.Errorf("compressing %w", err)
+	}
+
+	// Since we retry writes we need to track the total amount of accepted data
+	// across the various attempts.
+	accumulatedStats := WriteResponseStats{}
+
+	b := backoff.New(ctx, o.Backoff)
+	for {
+		rs, err := c.write(ctx, proto, payload, b.NumRetries())
+		accumulatedStats = accumulatedStats.Add(rs)
+		if err == nil {
+			// Success!
+			// TODO(bwplotka): Debug log with retry summary?
+			return accumulatedStats, nil
+		}
+
+		var retryableErr RetryableError
+		if !errors.As(err, &retryableErr) {
+			// TODO(bwplotka): More context in the error e.g. about retries.
+			return accumulatedStats, err
+		}
+
+		if !b.Ongoing() {
+			// TODO(bwplotka): More context in the error e.g. about retries.
+			return accumulatedStats, err
+		}
+
+		backoffDelay := b.NextDelay() + retryableErr.RetryAfter()
+		c.logger.Error("failed to send remote write request; retrying after backoff", "err", err, "backoff", backoffDelay)
+		select {
+		case <-ctx.Done():
+			// TODO(bwplotka): More context in the error e.g. about retries.
+			return WriteResponseStats{}, ctx.Err()
+		case <-time.After(backoffDelay):
+			// Retry.
+		}
+	}
+}
+
+func compressPayload(tmpbuf *[]byte, enc Compression, inp []byte) (compressed []byte, _ error) {
+	switch enc {
+	case SnappyBlockCompression:
+		compressed = snappy.Encode(*tmpbuf, inp)
+		if n := snappy.MaxEncodedLen(len(inp)); n > len(*tmpbuf) {
+			// grow the buffer for the next time.
+			*tmpbuf = make([]byte, n)
+		}
+		return compressed, nil
+	default:
+		return compressed, fmt.Errorf("Unknown compression scheme [%v]", enc)
+	}
+}
+
+func (c *Client) write(ctx context.Context, proto ProtoMsg, payload []byte, attempt int) (WriteResponseStats, error) {
+	httpReq, err := http.NewRequest(http.MethodPost, c.url, bytes.NewReader(payload))
+	if err != nil {
+		// Errors from NewRequest are from unparsable URLs, so are not
+		// recoverable.
+		return WriteResponseStats{}, err
+	}
+
+	httpReq.Header.Add("Content-Encoding", string(c.compr))
+	httpReq.Header.Set("Content-Type", ContentTypeHeader(proto))
+	httpReq.Header.Set("User-Agent", c.userAgent)
+	if proto == ProtoMsgV1 {
+		// Compatibility mode for 1.0.
+		httpReq.Header.Set(VersionHeader, Version1HeaderValue)
+	} else {
+		httpReq.Header.Set(VersionHeader, Version20HeaderValue)
+	}
+
+	if attempt > 0 {
+		httpReq.Header.Set("Retry-Attempt", strconv.Itoa(attempt))
+	}
+
+	httpResp, err := c.client.Do(httpReq.WithContext(ctx))
+	if err != nil {
+		// Errors from Client.Do are likely network errors, so recoverable.
+		return WriteResponseStats{}, RetryableError{err, defaultBackoff}
+	}
+	defer func() {
+		_, _ = io.Copy(io.Discard, httpResp.Body)
+		_ = httpResp.Body.Close()
+	}()
+
+	rs, err := parseWriteResponseStats(httpResp)
+	if err != nil {
+		c.logger.Warn("parsing rw write statistics failed; partial or no stats", "err", err)
+	}
+
+	if httpResp.StatusCode/100 == 2 {
+		return rs, nil
+	}
+
+	body, err := io.ReadAll(io.LimitReader(httpResp.Body, maxErrMsgLen))
+	err = fmt.Errorf("server returned HTTP status %s: %s", httpResp.Status, body)
+
+	if httpResp.StatusCode/100 == 5 ||
+		(c.retryOnRateLimit && httpResp.StatusCode == http.StatusTooManyRequests) {
+		return rs, RetryableError{err, retryAfterDuration(httpResp.Header.Get("Retry-After"))}
+	}
+	return rs, err
+}
+
+// retryAfterDuration returns the duration for the Retry-After header. In case of any errors, it
+// returns 0 as if the header was never supplied.
+func retryAfterDuration(t string) time.Duration {
+	parsedDuration, err := time.Parse(http.TimeFormat, t)
+	if err == nil {
+		return time.Until(parsedDuration)
+	}
+	// The duration can be in seconds.
+	d, err := strconv.Atoi(t)
+	if err != nil {
+		return 0
+	}
+	return time.Duration(d) * time.Second
+}