Switch to using per header field parsing for Go versions >= 1.24 (#1636)

* switch to using per header field parsing

* address review feedback

* update change log

* fix lint issue

* add depends on for the new probe

* Update internal/pkg/instrumentation/bpf/net/http/server/probe.go

Co-authored-by: Tyler Yahn <[email protected]>

* update change log

* Update changelog after 2.0

---------

Co-authored-by: Tyler Yahn <[email protected]>

Author: grcevski

CHANGELOG.md

@@ -8,6 +8,9 @@ OpenTelemetry Go Automatic Instrumentation adheres to [Semantic Versioning](http
 
 ## [Unreleased]
 
+### Added
+- Preemptively update instrumentation for `net/http` to support Go `1.24` when swiss maps are going to be added. ([#1636](https://github.com/open-telemetry/opentelemetry-go-instrumentation/pull/1636))
+
 ## [v0.20.0] - 2025-01-29
 
 ### Added

internal/include/utils.h

@@ -20,6 +20,18 @@ static __always_inline bool bpf_memcmp(char *s1, char *s2, s32 size)
     return true;
 }
 
+// assumes s2 is all lowercase
+static __always_inline int bpf_memicmp(const char *s1, const char *s2, s32 size) {
+    for (int i = 0; i < size; i++) {
+        if (s1[i] != s2[i] && s1[i] != (s2[i] - 32)) // compare with each uppercase character
+        {
+            return i + 1;
+        }
+    }
+
+    return 0;
+}
+
 static __always_inline void generate_random_bytes(unsigned char *buff, u32 size)
 {
     for (int i = 0; i < (size / 4); i++)

internal/pkg/instrumentation/bpf/net/http/server/bpf/probe.bpf.c

@@ -50,6 +50,14 @@ struct
     __uint(max_entries, MAX_CONCURRENT);
 } http_server_uprobes SEC(".maps");
 
+struct
+{
+    __uint(type, BPF_MAP_TYPE_LRU_HASH);
+    __type(key, void *);
+    __type(value, struct span_context);
+    __uint(max_entries, MAX_CONCURRENT);
+} http_server_context_headers SEC(".maps");
+
 struct
 {
     __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
@@ -84,11 +92,13 @@ volatile const bool pattern_path_supported;
 // In case pattern handlers are supported the following offsets will be used:
 volatile const u64 req_pat_pos;
 volatile const u64 pat_str_pos;
+// A flag indicating whether the Go version is using swiss maps
+volatile const bool swiss_maps_used;
 
 // Extracts the span context from the request headers by looking for the 'traceparent' header.
 // Fills the parent_span_context with the extracted span context.
 // Returns 0 on success, negative value on error.
-static __always_inline long extract_context_from_req_headers(void *headers_ptr_ptr, struct span_context *parent_span_context)
+static __always_inline long extract_context_from_req_headers_go_map(void *headers_ptr_ptr, struct span_context *parent_span_context)
 {
     void *headers_ptr;
     long res;
@@ -178,6 +188,23 @@ static __always_inline long extract_context_from_req_headers(void *headers_ptr_p
     return -1;
 }
 
+static __always_inline long extract_context_from_req_headers_pre_parsed(void *key, struct span_context *parent_span_context) {
+    struct span_context *parsed_header_context = bpf_map_lookup_elem(&http_server_context_headers, &key);
+    if (!parsed_header_context) {
+        return -1;
+    }
+
+    __builtin_memcpy(parent_span_context, parsed_header_context, sizeof(struct span_context));
+    return 0;
+}
+
+static __always_inline long extract_context_from_req_headers(void *key, struct span_context *parent_span_context) {
+    if (swiss_maps_used) {
+        return extract_context_from_req_headers_pre_parsed(key, parent_span_context);
+    }
+    return extract_context_from_req_headers_go_map(key, parent_span_context);
+}
+
 static __always_inline void read_go_string(void *base, int offset, char *output, int maxLen, const char *errorMsg) {
     void *ptr = (void *)(base + offset);
     if (!get_go_string_from_user_ptr(ptr, output, maxLen)) {
@@ -225,8 +252,17 @@ int uprobe_serverHandler_ServeHTTP(struct pt_regs *ctx)
         .psc = &http_server_span->psc,
         .sc = &http_server_span->sc,
         .get_parent_span_context_fn = extract_context_from_req_headers,
-        .get_parent_span_context_arg = (void*)(req_ptr + headers_ptr_pos),
     };
+
+    // If Go is using swiss maps, we currently rely on the uretprobe setup
+    // on readContinuedLineSlice to store the parsed value in a map, which
+    // we query with the same goroutine/context key.
+    if (swiss_maps_used) {
+        start_span_params.get_parent_span_context_arg = key;
+    } else {
+        start_span_params.get_parent_span_context_arg = (void*)(req_ptr + headers_ptr_pos);
+    }
+
     start_span(&start_span_params);
 
     bpf_map_update_elem(&http_server_uprobes, &key, uprobe_data, 0);
@@ -246,6 +282,7 @@ int uprobe_serverHandler_ServeHTTP_Returns(struct pt_regs *ctx) {
     struct uprobe_data_t *uprobe_data = bpf_map_lookup_elem(&http_server_uprobes, &key);
     if (uprobe_data == NULL) {
         bpf_printk("uprobe/HandlerFunc_ServeHTTP_Returns: entry_state is NULL");
+        bpf_map_delete_elem(&http_server_context_headers, &key);
         return 0;
     }
 
@@ -280,5 +317,31 @@ int uprobe_serverHandler_ServeHTTP_Returns(struct pt_regs *ctx) {
 
     stop_tracking_span(&http_server_span->sc, &http_server_span->psc);
     bpf_map_delete_elem(&http_server_uprobes, &key);
+    bpf_map_delete_elem(&http_server_context_headers, &key);
+    return 0;
+}
+
+// This instrumentation attaches uprobe to the following function:
+// func (r *Reader) readContinuedLineSlice(lim int64, validateFirstLine func([]byte) error) ([]byte, error) {
+SEC("uprobe/textproto_Reader_readContinuedLineSlice")
+int uprobe_textproto_Reader_readContinuedLineSlice_Returns(struct pt_regs *ctx) {
+    struct go_iface go_context = {0};
+    get_Go_context(ctx, 4, ctx_ptr_pos, false, &go_context);
+    void *key = get_consistent_key(ctx, go_context.data);
+
+    u64 len = (u64)GO_PARAM2(ctx);
+    u8 *buf = (u8 *)GO_PARAM1(ctx);
+
+    if (len >= (W3C_KEY_LENGTH + W3C_VAL_LENGTH + 2)) {
+        u8 temp[W3C_KEY_LENGTH + W3C_VAL_LENGTH + 2];
+        bpf_probe_read(temp, sizeof(temp), buf);
+
+        if (!bpf_memicmp((const char *)temp, "traceparent: ", W3C_KEY_LENGTH + 2)) {
+            struct span_context parent_span_context = {};
+            w3c_string_to_span_context((char *)(temp + W3C_KEY_LENGTH + 2), &parent_span_context);            
+            bpf_map_update_elem(&http_server_context_headers, &key, &parent_span_context, BPF_ANY);
+        }
+    }
+
     return 0;
 }

internal/pkg/instrumentation/bpf/net/http/server/bpf_arm64_bpfel.go

@@ -28,9 +28,19 @@ import (
 
 const (
 	// pkg is the package being instrumented.
-	pkg = "net/http"
+	pkg            = "net/http"
+	minGoSwissMaps = "1.24.0"
 )
 
+var goWithSwissMaps = probe.PackageConstrainst{
+	Package: "std",
+	Constraints: version.MustConstraints(
+		version.NewConstraint(">= " + minGoSwissMaps),
+	),
+	// Don't warn, we have a backup path.
+	FailureMode: probe.FailureModeIgnore,
+}
+
 // New returns a new [probe.Probe].
 func New(logger *slog.Logger, version string) probe.Probe {
 	id := probe.ID{
@@ -102,13 +112,22 @@ func New(logger *slog.Logger, version string) probe.Probe {
 					MinVersion: patternPathMinVersion,
 				},
 				patternPathSupportedConst{},
+				swissMapsUsedConst{},
 			},
 			Uprobes: []*probe.Uprobe{
 				{
 					Sym:         "net/http.serverHandler.ServeHTTP",
 					EntryProbe:  "uprobe_serverHandler_ServeHTTP",
 					ReturnProbe: "uprobe_serverHandler_ServeHTTP_Returns",
 				},
+				{
+					Sym:         "net/textproto.(*Reader).readContinuedLineSlice",
+					ReturnProbe: "uprobe_textproto_Reader_readContinuedLineSlice_Returns",
+					PackageConstrainsts: []probe.PackageConstrainst{
+						goWithSwissMaps,
+					},
+					DependsOn: []string{"net/http.serverHandler.ServeHTTP"},
+				},
 			},
 			SpecFn: loadBpf,
 		},
@@ -130,6 +149,14 @@ func (c patternPathSupportedConst) InjectOption(td *process.TargetDetails) (inje
 	return inject.WithKeyValue("pattern_path_supported", isPatternPathSupported), nil
 }
 
+type swissMapsUsedConst struct{}
+
+func (c swissMapsUsedConst) InjectOption(td *process.TargetDetails) (inject.Option, error) {
+	minGoSwissMapsVersion := version.Must(version.NewVersion(minGoSwissMaps))
+	isUsingGoSwissMaps := td.GoVersion.GreaterThanOrEqual(minGoSwissMapsVersion)
+	return inject.WithKeyValue("swiss_maps_used", isUsingGoSwissMaps), nil
+}
+
 // event represents an event in an HTTP server during an HTTP
 // request-response.
 type event struct {

internal/pkg/instrumentation/bpf/net/http/server/bpf_x86_bpfel.go

@@ -188,7 +188,7 @@ func (i *Base[BPFObj, BPFEvent]) loadUprobes(exec *link.Executable, td *process.
 				logFn = i.Logger.Warn
 			default:
 				// Unknown and FailureModeError.
-				return fmt.Errorf("uprobe %s package constraint (%s) not meet", up.Sym, pc.Constraints.String())
+				return fmt.Errorf("uprobe %s package constraint (%s) not met, version %v", up.Sym, pc.Constraints.String(), td.Modules[pc.Package])
 			}
 
 			logFn(
@@ -197,6 +197,7 @@ func (i *Base[BPFObj, BPFEvent]) loadUprobes(exec *link.Executable, td *process.
 				"symbol", up.Sym,
 				"package", pc.Package,
 				"constraint", pc.Constraints.String(),
+				"version", td.Modules[pc.Package],
 			)
 
 			skip = true