Eino: Document Loader guide

type Loader interface {
    Load(ctx context.Context, src Source, opts ...LoaderOption) ([]*schema.Document, error)
}

type Source struct {
    URI string
}

type Document struct {
    // ID is the unique identifier of the document
    ID string
    // Content is the content of the document
    Content string
    // MetaData is used to store metadata information of the document
    MetaData map[string]any
}

import (
    "github.com/cloudwego/eino/components/document"
    "github.com/cloudwego/eino-ext/components/document/loader/file"
)

// Initialize loader (take file loader as an example)
loader, _ := file.NewFileLoader(ctx, &file.FileLoaderConfig{
    // Configuration parameters
    UseNameAsID: true,
})

// Load document
filePath := "../../testdata/test.md"
docs, _ := loader.Load(ctx, document.Source{
    URI: filePath,
})

log.Printf("doc content: %v", docs[0].Content)

// Use in Chain
chain := compose.NewChain[document.Source, []*schema.Document]()
chain.AppendLoader(loader)

// Compile and run
runnable, _ := chain.Compile()

result, _ := runnable.Invoke(ctx, input)

// Use in Graph
graph := compose.NewGraph[string, []*schema.Document]()
graph.AddLoaderNode("loader_node", loader)

import (
    "github.com/cloudwego/eino/callbacks"
    "github.com/cloudwego/eino/components/document"
    "github.com/cloudwego/eino/compose"
    "github.com/cloudwego/eino/schema"
    callbacksHelper "github.com/cloudwego/eino/utils/callbacks"

    "github.com/cloudwego/eino-ext/components/document/loader/file"
)

// Create callback handler
handler := &callbacksHelper.LoaderCallbackHandler{
    OnStart: func(ctx context.Context, info *callbacks.RunInfo, input *document.LoaderCallbackInput) context.Context {
       log.Printf("start loading docs...: %s\n", input.Source.URI)
       return ctx
    },
    OnEnd: func(ctx context.Context, info *callbacks.RunInfo, output *document.LoaderCallbackOutput) context.Context {
       log.Printf("complete loading docs，total loaded docs: %d\n", len(output.Docs))
       return ctx
    },
    // OnError
}

// Use callback handler
helper := callbacksHelper.NewHandlerHelper().
    Loader(handler).
    Handler()

chain := compose.NewChain[document.Source, []*schema.Document]()
chain.AppendLoader(loader)
// Use at runtime
run, _ := chain.Compile(ctx)

outDocs, _ := run.Invoke(ctx, document.Source{
    URI: filePath,
}, compose.WithCallbacks(helper))

log.Printf("doc content: %v", outDocs[0].Content)

// Define the options struct
type MyLoaderOptions struct {
    Timeout time.Duration
    RetryCount int
}

// Define option functions
func WithTimeout(timeout time.Duration) document.LoaderOption {
    return document.WrapLoaderImplSpecificOptFn(func(o *MyLoaderOptions) {
        o.Timeout = timeout
    })
}

func WithRetryCount(count int) document.LoaderOption {
    return document.WrapLoaderImplSpecificOptFn(func(o *MyLoaderOptions) {
        o.RetryCount = count
    })
}

// These are the callback input and output defined by the loader component. Implementations should satisfy the parameter meanings.
type LoaderCallbackInput struct {
    Source Source
    Extra map[string]any
}

type LoaderCallbackOutput struct {
    Source Source
    Docs []*schema.Document
    Extra map[string]any
}

import (
    "github.com/cloudwego/eino/callbacks"
    "github.com/cloudwego/eino/components/document"
    "github.com/cloudwego/eino/schema"
)

func NewCustomLoader(config *Config) (*CustomLoader, error) {
    return & CustomLoader {
       timeout: config.DefaultTimeout,
       retryCount: config.DefaultRetryCount,
    }, nil
}

type CustomLoader struct {
    timeout time.Duration
    retryCount int
}

type Config struct {
    DefaultTimeout time.Duration
    DefaultRetryCount int
}

func (l *CustomLoader) Load(ctx context.Context, src document.Source, opts ...document.LoaderOption) ([]*schema.Document, error) {
    // 1. Handle options
    options := &customLoaderOptions{
       Timeout: l.timeout,
       RetryCount: l.retryCount,
    }
    options = document.GetLoaderImplSpecificOptions(options, opts...)
    var err error

    // 2. Handle errors and trigger error callbacks
    defer func() {
       if err != nil {
          callbacks.OnError(ctx, err)
       }
    }()

    // 3. Trigger pre-load callback
    ctx = callbacks.OnStart(ctx, &document.LoaderCallbackInput{
       Source: src,
    })

    // 4. Execute load logic
    docs, err := l.doLoad(ctx, src, options)

    if err != nil {
       return nil, err
    }

    ctx = callbacks.OnEnd(ctx, &document.LoaderCallbackOutput{
       Source: src,
       Docs:   docs,
    })

    return docs, nil
}

func (l *CustomLoader) doLoad(ctx context.Context, src document.Source, opts *customLoaderOptions) ([]*schema.Document, error) {
    // Implement document load logic
    // 1. Load document content
    // 2. Construct Document objects, ensuring to save important information such as document source in MetaData
    return []*schema.Document{{
       Content: "Hello World",
    }}, nil
}