flow: decouple component HTTP API (#4361)

* component: add ParseID as a common function

Splitting a global component ID into its module ID and local ID will be
a commonly used utility which makes sense to include as part of the API
for components.

* service/http: cross-module component handler

This changes the component handler for the HTTP service to be able to
handle requests across all modules from the same root Flow controller.

* flow: remove unnecessary HTTP handler

This removes the HTTP handlers from the Flow controller and modules, as
all HTTP handlers are now handled centrally from the HTTP service.

component/component_provider.go

@@ -2,25 +2,37 @@ package component
 
 import (
 	"encoding/json"
+	"errors"
+	"strings"
 	"time"
 
 	"github.com/grafana/agent/pkg/river/encoding/riverjson"
 )
 
+var (
+	// ErrComponentNotFound is returned by [Provider.GetComponent] when the
+	// specified component isn't found.
+	ErrComponentNotFound = errors.New("component not found")
+
+	// ErrModuleNotFound is returned by [Provider.ListComponents] when the
+	// specified module isn't found.
+	ErrModuleNotFound = errors.New("module not found")
+)
+
 // A Provider is a system which exposes a list of running components.
 type Provider interface {
 	// GetComponent returns information about an individual running component
 	// given its global ID. The provided opts field configures how much detail to
 	// return; see [InfoOptions] for more information.
 	//
-	// GetComponent returns an error if a component is not found.
+	// GetComponent returns ErrComponentNotFound if a component is not found.
 	GetComponent(id ID, opts InfoOptions) (*Info, error)
 
 	// ListComponents returns the list of active components. The provided opts
 	// field configures how much detail to return; see [InfoOptions] for more
 	// information.
 	//
-	// Returns an error if the provided moduleID doesn't exist.
+	// Returns ErrModuleNotFound if the provided moduleID doesn't exist.
 	ListComponents(moduleID string, opts InfoOptions) ([]*Info, error)
 }
 
@@ -30,6 +42,20 @@ type ID struct {
 	LocalID  string // Local ID of the component, unique to the module it is running in.
 }
 
+// ParseID parses an input string of the form "LOCAL_ID" or
+// "MODULE_ID/LOCAL_ID" into an ID. The final slash character is used to
+// separate the ModuleID and LocalID.
+func ParseID(input string) ID {
+	slashIndex := strings.LastIndexByte(input, '/')
+	if slashIndex == -1 {
+		return ID{LocalID: input}
+	}
+	return ID{
+		ModuleID: input[:slashIndex],
+		LocalID:  input[slashIndex+1:],
+	}
+}
+
 // InfoOptions is used by to determine how much information to return with
 // [Info].
 type InfoOptions struct {

component/module/file/file.go

@@ -2,7 +2,6 @@ package file
 
 import (
 	"context"
-	"net/http"
 	"sync"
 
 	"go.uber.org/atomic"
@@ -55,7 +54,6 @@ type Component struct {
 var (
 	_ component.Component       = (*Component)(nil)
 	_ component.HealthComponent = (*Component)(nil)
-	_ component.HTTPComponent   = (*Component)(nil)
 )
 
 // New creates a new module.file component.
@@ -140,11 +138,6 @@ func (c *Component) Update(args component.Arguments) error {
 	return c.mod.LoadFlowContent(newArgs.Arguments, c.getContent().Value)
 }
 
-// Handler implements component.HTTPComponent.
-func (c *Component) Handler() http.Handler {
-	return c.mod.HTTPHandler()
-}
-
 // CurrentHealth implements component.HealthComponent.
 func (c *Component) CurrentHealth() component.Health {
 	leastHealthy := component.LeastHealthy(

component/module/git/git.go

@@ -3,7 +3,6 @@ package git
 
 import (
 	"context"
-	"net/http"
 	"path/filepath"
 	"reflect"
 	"sync"
@@ -70,7 +69,6 @@ type Component struct {
 var (
 	_ component.Component       = (*Component)(nil)
 	_ component.HealthComponent = (*Component)(nil)
-	_ component.HTTPComponent   = (*Component)(nil)
 )
 
 // New creates a new module.git component.
@@ -238,11 +236,6 @@ func (c *Component) CurrentHealth() component.Health {
 	return component.LeastHealthy(c.health, c.mod.CurrentHealth())
 }
 
-// Handler implements component.HTTPComponent.
-func (c *Component) Handler() http.Handler {
-	return c.mod.HTTPHandler()
-}
-
 // DebugInfo implements component.DebugComponent.
 func (c *Component) DebugInfo() interface{} {
 	type DebugInfo struct {

component/module/module.go

@@ -3,7 +3,6 @@ package module
 import (
 	"context"
 	"fmt"
-	"net/http"
 	"sync"
 	"time"
 
@@ -72,11 +71,6 @@ func (c *ModuleComponent) CurrentHealth() component.Health {
 	return c.health
 }
 
-// HTTPHandler returns the underlying module handle for the UI.
-func (c *ModuleComponent) HTTPHandler() http.Handler {
-	return c.mod.ComponentHandler()
-}
-
 // SetHealth contains the implementation details for setHealth in a module component.
 func (c *ModuleComponent) setHealth(h component.Health) {
 	c.mut.Lock()

component/module/string/string.go

@@ -2,7 +2,6 @@ package string
 
 import (
 	"context"
-	"net/http"
 
 	"github.com/grafana/agent/component"
 	"github.com/grafana/agent/component/module"
@@ -39,7 +38,6 @@ type Component struct {
 var (
 	_ component.Component       = (*Component)(nil)
 	_ component.HealthComponent = (*Component)(nil)
-	_ component.HTTPComponent   = (*Component)(nil)
 )
 
 // New creates a new module.string component.
@@ -71,10 +69,6 @@ func (c *Component) Update(args component.Arguments) error {
 	return c.mod.LoadFlowContent(newArgs.Arguments, newArgs.Content.Value)
 }
 
-func (c *Component) Handler() http.Handler {
-	return c.mod.HTTPHandler()
-}
-
 // CurrentHealth implements component.HealthComponent.
 func (c *Component) CurrentHealth() component.Health {
 	return c.mod.CurrentHealth()

component/registry.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"net"
-	"net/http"
 	"reflect"
 	"strings"
 
@@ -53,10 +52,6 @@ type Module interface {
 	// Run blocks until the provided context is canceled. The ID of a module as defined in
 	// ModuleController.NewModule will not be released until Run returns.
 	Run(context.Context)
-
-	// ComponentHandler returns an HTTP handler which exposes endpoints of
-	// components managed by the Module.
-	ComponentHandler() http.Handler
 }
 
 // ExportFunc is used for onExport of the Module

pkg/flow/flow_components.go

@@ -16,7 +16,7 @@ func (f *Flow) GetComponent(id component.ID, opts component.InfoOptions) (*compo
 	if id.ModuleID != "" {
 		mod, ok := f.modules.Get(id.ModuleID)
 		if !ok {
-			return nil, fmt.Errorf("component %q does not exist", id)
+			return nil, component.ErrComponentNotFound
 		}
 
 		return mod.f.GetComponent(component.ID{LocalID: id.LocalID}, opts)
@@ -26,7 +26,7 @@ func (f *Flow) GetComponent(id component.ID, opts component.InfoOptions) (*compo
 
 	node := graph.GetByID(id.LocalID)
 	if node == nil {
-		return nil, fmt.Errorf("component %q does not exist", id)
+		return nil, component.ErrComponentNotFound
 	}
 
 	cn, ok := node.(*controller.ComponentNode)
@@ -45,7 +45,7 @@ func (f *Flow) ListComponents(moduleID string, opts component.InfoOptions) ([]*c
 	if moduleID != "" {
 		mod, ok := f.modules.Get(moduleID)
 		if !ok {
-			return nil, fmt.Errorf("module %q does not exist", moduleID)
+			return nil, component.ErrModuleNotFound
 		}
 
 		return mod.f.ListComponents("", opts)

pkg/flow/module.go

@@ -3,11 +3,9 @@ package flow
 import (
 	"context"
 	"fmt"
-	"net/http"
 	"path"
 	"sync"
 
-	"github.com/gorilla/mux"
 	"github.com/grafana/agent/component"
 	"github.com/grafana/agent/pkg/cluster"
 	"github.com/grafana/agent/pkg/flow/internal/controller"
@@ -144,22 +142,6 @@ func (c *module) Run(ctx context.Context) {
 	c.f.Run(ctx)
 }
 
-// ComponentHandler returns an HTTP handler which exposes endpoints of
-// components managed by the underlying flow system.
-func (c *module) ComponentHandler() (_ http.Handler) {
-	r := mux.NewRouter()
-
-	r.PathPrefix("/{id}/").HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		// Re-add the full path to ensure that nested controllers propagate
-		// requests properly.
-		r.URL.Path = path.Join(c.o.HTTPPath, r.URL.Path)
-
-		c.f.ComponentHandler().ServeHTTP(w, r)
-	})
-
-	return r
-}
-
 // moduleControllerOptions holds static options for module controller.
 type moduleControllerOptions struct {
 	// Logger to use for controller logs and components. A no-op logger will be

service/http/http.go

@@ -132,7 +132,7 @@ func (s *Service) Run(ctx context.Context, host service.Host) error {
 		r.PathPrefix("/debug/pprof").Handler(http.DefaultServeMux)
 	}
 
-	r.PathPrefix(s.componentHttpPathPrefix + "{id}/").Handler(s.componentHandler(host))
+	r.PathPrefix(s.componentHttpPathPrefix).Handler(s.componentHandler(host))
 
 	if s.node != nil {
 		cr, ch := s.node.Handler()
@@ -196,20 +196,18 @@ func (s *Service) Run(ctx context.Context, host service.Host) error {
 }
 
 func (s *Service) componentHandler(host service.Host) http.HandlerFunc {
-	// TODO(rfratto): make this work across modules. Right now this handler
-	// only works for the top-level module, and forwards requests to inner
-	// modules.
-	//
-	// This means that the Flow controller still has HTTP logic until this is
-	// resolved.
-
 	return func(w http.ResponseWriter, r *http.Request) {
-		vars := mux.Vars(r)
-		id := vars["id"]
+		// Trim the path prefix to get our full path.
+		trimmedPath := strings.TrimPrefix(r.URL.Path, s.componentHttpPathPrefix)
+
+		// splitURLPath should only fail given an unexpected path.
+		componentID, componentPath, err := splitURLPath(host, trimmedPath)
+		if err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+			fmt.Fprintf(w, "failed to parse URL path %q: %s\n", r.URL.Path, err)
+		}
 
-		// We pass no options in component.InfoOptions, because we're only
-		// interested in the component instance.
-		info, err := host.GetComponent(component.ID{LocalID: id}, component.InfoOptions{})
+		info, err := host.GetComponent(componentID, component.InfoOptions{})
 		if err != nil {
 			w.WriteHeader(http.StatusNotFound)
 			return
@@ -226,9 +224,9 @@ func (s *Service) componentHandler(host service.Host) http.HandlerFunc {
 			return
 		}
 
-		// Remove prefix from path, so each component can handle paths from their
-		// own root path.
-		r.URL.Path = strings.TrimPrefix(r.URL.Path, path.Join(s.componentHttpPathPrefix, id))
+		// Send just the remaining path to our component so each component can
+		// handle paths from their own root path.
+		r.URL.Path = componentPath
 		handler.ServeHTTP(w, r)
 	}
 }