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Graceful error handling for host function calls from guest modules #89

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Graceful error handling for host function calls from guest modules #89

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b62b6c4
Support graceful error handling for host functions
clarkmcc Dec 3, 2024
30c6df4
Use existing `error_set` function for passing host errors to guest
clarkmcc Dec 4, 2024
3a64cc0
Cleaned up based on PR feedback
clarkmcc Dec 4, 2024
261a41b
wip approach to signal host->host errors
clarkmcc Dec 4, 2024
78228e7
Shore up graceful host function error handling
clarkmcc Dec 5, 2024
ebfdc41
Fixed potential panic point if errPrefix were to be change
clarkmcc Dec 6, 2024
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10 changes: 4 additions & 6 deletions extism.go
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Original file line number Diff line number Diff line change
Expand Up @@ -110,12 +110,10 @@ type Plugin struct {
close []func(ctx context.Context) error
extism api.Module

//Runtime *Runtime
//Main Module
module api.Module
Timeout time.Duration
Config map[string]string
// NOTE: maybe we can have some nice methods for getting/setting vars
hostFuncError error
module api.Module
Timeout time.Duration
Config map[string]string
Var map[string][]byte
AllowedHosts []string
AllowedPaths map[string]string
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22 changes: 20 additions & 2 deletions host.go
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Original file line number Diff line number Diff line change
Expand Up @@ -109,6 +109,24 @@ func (p *Plugin) currentPlugin() *CurrentPlugin {
return &CurrentPlugin{p}
}

// SetHostFunctionError allows the host function to set an error that will be
// gracefully returned by extism guest modules.
func (p *CurrentPlugin) SetHostFunctionError(ctx context.Context, err error) {
if err == nil {
return
}

offset, err := p.WriteString(err.Error())
if err != nil {
panic(fmt.Sprintf("failed to write error message to memory: %v", err))
}

_, err = p.plugin.extism.ExportedFunction("error_set").Call(ctx, offset)
if err != nil {
panic(fmt.Sprintf("failed to set error: %v", err))
}
}

func (p *CurrentPlugin) Log(level LogLevel, message string) {
p.plugin.Log(level, message)
}
Expand Down Expand Up @@ -237,7 +255,7 @@ func defineCustomHostFunctions(builder wazero.HostModuleBuilder, funcs []HostFun
// See: https://github.com/extism/go-sdk/issues/5#issuecomment-1666774486
closure := f.stackCallback

builder.NewFunctionBuilder().WithGoFunction(api.GoFunc(func(ctx context.Context, stack []uint64) {
builder.NewFunctionBuilder().WithGoModuleFunction(api.GoModuleFunc(func(ctx context.Context, m api.Module, stack []uint64) {
if plugin, ok := ctx.Value(PluginCtxKey("plugin")).(*Plugin); ok {
closure(ctx, &CurrentPlugin{plugin}, stack)
return
Expand Down Expand Up @@ -306,7 +324,7 @@ func instantiateEnvModule(ctx context.Context, rt wazero.Runtime) (api.Module, e
WithGoModuleFunction(api.GoModuleFunc(store_u64), []ValueType{ValueTypeI64, ValueTypeI64}, []ValueType{}).
Export("store_u64")

hostFunc := func(name string, f interface{}) {
hostFunc := func(name string, f any) {
builder.NewFunctionBuilder().WithFunc(f).Export(name)
}

Expand Down