Carlos Florêncio
86 lines
2.4 KiB
Go
86 lines
2.4 KiB
Go
package webapp
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import (
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"bytes"
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"encoding/json"
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"fmt"
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"io/fs"
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)
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const bootPayloadGlobal = "window.__KANDEV_BOOT_PAYLOAD__"
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const debugGlobalAssignment = "window.__KANDEV_DEBUG=true;"
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const maxInt = int(^uint(0) >> 1)
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var headCloseTag = []byte("</head>")
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// RenderShell reads indexPath from assets and injects the boot payload before
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// </head>. The assets FS can be an embedded Vite dist in production or an
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// in-memory filesystem in tests.
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func RenderShell(assets fs.FS, indexPath string, payload BootPayload) ([]byte, error) {
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indexHTML, err := fs.ReadFile(assets, indexPath)
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if err != nil {
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return nil, fmt.Errorf("read web shell: %w", err)
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}
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return RenderShellHTML(indexHTML, payload)
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}
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// RenderShellHTML injects the boot payload into an already-loaded HTML shell.
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// Dev mode uses this with Vite's in-memory index.html.
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func RenderShellHTML(indexHTML []byte, payload BootPayload) ([]byte, error) {
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script, err := BootPayloadScript(payload)
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if err != nil {
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return nil, err
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}
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return injectBeforeHeadClose(indexHTML, script), nil
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}
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// BootPayloadScript serializes payload into an inline script safe to embed in
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// HTML. encoding/json escapes '<', '>', and '&', which prevents a state value
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// from closing the script tag.
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func BootPayloadScript(payload BootPayload) ([]byte, error) {
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data, err := json.Marshal(payload)
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if err != nil {
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return nil, fmt.Errorf("marshal boot payload: %w", err)
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}
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debugPrefix := ""
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if payload.Runtime.Debug {
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debugPrefix = debugGlobalAssignment
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}
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script := make([]byte, 0, bytesCapacity(len(data), len(debugPrefix), len(bootPayloadGlobal), 32))
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script = append(script, "<script>"...)
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script = append(script, debugPrefix...)
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script = append(script, bootPayloadGlobal...)
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script = append(script, "="...)
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script = append(script, data...)
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script = append(script, ";</script>"...)
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return script, nil
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}
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func injectBeforeHeadClose(indexHTML, script []byte) []byte {
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idx := bytes.Index(indexHTML, headCloseTag)
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if idx < 0 {
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out := make([]byte, 0, bytesCapacity(len(indexHTML), len(script)))
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out = append(out, script...)
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out = append(out, indexHTML...)
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return out
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}
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out := make([]byte, 0, bytesCapacity(len(indexHTML), len(script)))
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out = append(out, indexHTML[:idx]...)
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out = append(out, script...)
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out = append(out, indexHTML[idx:]...)
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return out
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}
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func bytesCapacity(parts ...int) int {
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total := 0
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for _, part := range parts {
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if part > maxInt-total {
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return 0
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}
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total += part
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}
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return total
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}
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