feat: add environment variables support for command execution

cmd/capture.go

@@ -26,6 +26,7 @@ import (
 )
 
 var functionSymbols string
+var envVars []string
 var commandOutput bool
 var commandError bool
 var libbpfOutput bool
@@ -66,7 +67,7 @@ by passing the function name symbol and the binary args.
 			errorCh := make(chan error)
 			ctx := context.Background()
 
-			ebpf, err := captor.InitProbes(functionSymbol, args, opts)
+			ebpf, err := captor.InitProbes(functionSymbol, args, envVars, opts)
 			if err != nil {
 				return fmt.Errorf("error setting up ebpf module: %w", err)
 			}
@@ -100,6 +101,7 @@ func init() {
 
 	captureCmd.Flags().StringVarP(&functionSymbols, "functions", "f", "", "Name of the function symbols to be traced")
 	captureCmd.MarkFlagRequired("functions")
+	captureCmd.Flags().StringSliceVarP(&envVars, "env-vars", "E", []string{}, "Additional environment variables to pass to the executed command")
 
 	captureCmd.Flags().BoolVarP(&commandOutput, "include-cmd-stdout", "c", false, "Include the executed command output")
 	captureCmd.Flags().BoolVarP(&commandError, "include-cmd-stderr", "e", false, "Include the executed command error")

cmd/hunt.go

@@ -84,7 +84,7 @@ var huntCmd = &cobra.Command{
 				errorCh := make(chan error)
 				ctx := context.Background()
 
-				ebpf, err := captor.InitProbes(functionSymbol, captureArgs, opts)
+				ebpf, err := captor.InitProbes(functionSymbol, captureArgs, envVars, opts)
 				if err != nil {
 					return fmt.Errorf("error setting up ebpf module: %w", err)
 				}

docs/tutorials.md

@@ -88,6 +88,18 @@ To do so, you have the `--dump-interval/-i` flag available. This flag gives you
 harpoon capture -f main.main --dump-interval 2 -- ./binary_name
 ```
 
+## Tracing a program that requires environment variables to run
+
+`harpoon` provides support to pass environment variables to the executed command.
+
+This is really useful to trace the command changing its behaviour through env vars.
+
+Here's how you can pass multiple env vars to the executed command:
+
+```sh
+harpoon capture -f main.main -E "VAR1=value1" -E "VAR2=value2" -- ./binary_name
+```
+
 ## Tracing from unit-tests
 
 `harpoon` has additional commands other than `capture`. The commands are `analyze` and `hunt`.

internal/ebpf/probesfacade/captor/capture.go

@@ -46,12 +46,13 @@ type ebpfSetup struct {
 	lostCh   chan uint64
 	opts     CaptureOptions
 	cmd      []string
+	env      []string
 }
 
 // InitProbes setup the ebpf module attaching probes and tracepoints
 // to the ebpf program.
 // Returns the ebpfSetup struct in case of seccess, an error in case of failure.
-func InitProbes(functionSymbol string, cmdArgs []string, opts CaptureOptions) (*ebpfSetup, error) {
+func InitProbes(functionSymbol string, cmdArgs []string, env []string, opts CaptureOptions) (*ebpfSetup, error) {
 	if len(cmdArgs) == 0 {
 		return nil, errors.New("error no arguments provided, at least 1 argument is required")
 	}
@@ -138,6 +139,7 @@ func InitProbes(functionSymbol string, cmdArgs []string, opts CaptureOptions) (*
 		lostCh:   lostChannel,
 		opts:     opts,
 		cmd:      cmdArgs,
+		env:      env,
 	}, nil
 }
 
@@ -173,6 +175,7 @@ func (ebpf *ebpfSetup) Capture(ctx context.Context, resultCh chan []uint32, erro
 	// running command to trace its syscalls
 	go executor.Run(
 		ebpf.cmd,
+		ebpf.env,
 		ebpf.opts.CommandOutput,
 		ebpf.opts.CommandError,
 		&wg,

internal/executor/exec.go

@@ -10,12 +10,18 @@ import (
 
 // Run execute the command and wait for its end.
 // The cmdOutput argument is used to print the command output.
-func Run(cmd []string, cmdOutput, cmdError bool, wg *sync.WaitGroup, outputCh, errorCh chan<- string) {
+func Run(cmd []string, envVars []string, cmdOutput, cmdError bool, wg *sync.WaitGroup, outputCh, errorCh chan<- string) {
 	defer func() {
 		wg.Done()
 	}()
 
 	command := exec.Command(cmd[0], cmd[1:]...)
+	// assign custom env variables to the command
+	env := os.Environ()
+	if len(envVars) > 0 {
+		env = append(env, envVars...)
+	}
+	command.Env = env
 	stdout, _ := command.StdoutPipe()
 	stderr, _ := command.StderrPipe()
 

tests/integration.txtar

@@ -52,6 +52,9 @@ stdout 'write'
 exec harpoon capture -f main.main -c -- ./bin/example-app coin
 stdout 'stdout: \[flip coin\]'
 
+exec harpoon capture -f main.main -E "VAR1=0" -E "VAR2=1" -- ./bin/example-app coin
+stdout 'write'
+
 exec harpoon capture -f main.main -e -- ./bin/example-app streams
 stdout 'stderr: 0'