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A page on another origin can POST text/plain or a form without a CORS preflight, so its visitors' browsers could store reports although the server sends no CORS headers. decodeJSON now refuses a request whose Content-Type is not application/json (parameters such as charset allowed), and the report handler answers it 415 with the usual error body, storing nothing. A JSON POST waits for the preflight, which only an origin in CORS_ALLOWED_ORIGINS passes; the page already sends application/json. Model: opus-5-5
111 lines
2.7 KiB
Go
111 lines
2.7 KiB
Go
// Package handlers implements HTTP request handlers for the
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// netwatch-server API.
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package handlers
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import (
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"context"
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"encoding/json"
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"errors"
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"log/slog"
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"mime"
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"net/http"
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"sneak.berlin/go/netwatch/internal/globals"
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"sneak.berlin/go/netwatch/internal/healthcheck"
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"sneak.berlin/go/netwatch/internal/logger"
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"sneak.berlin/go/netwatch/internal/reportbuf"
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"go.uber.org/fx"
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)
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const jsonContentType = "application/json; charset=utf-8"
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// errNotJSON is what decodeJSON returns for a request whose
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// Content-Type is not application/json.
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var errNotJSON = errors.New("content type is not application/json")
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// reportAppender is the subset of the report buffer the handlers
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// depend on. Defining it here keeps the storage failure path
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// exercisable with a stub in tests.
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type reportAppender interface {
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Append(v any) error
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}
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// Params defines the dependencies for Handlers.
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type Params struct {
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fx.In
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Buffer *reportbuf.Buffer
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Globals *globals.Globals
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Healthcheck *healthcheck.Healthcheck
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Logger *logger.Logger
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}
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// Handlers provides HTTP handler factories for all endpoints.
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type Handlers struct {
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buf reportAppender
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hc *healthcheck.Healthcheck
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log *slog.Logger
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params *Params
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}
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// New creates a Handlers instance.
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func New(
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lc fx.Lifecycle,
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params Params,
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) (*Handlers, error) {
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s := new(Handlers)
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s.buf = params.Buffer
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s.params = ¶ms
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s.log = params.Logger.Get()
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s.hc = params.Healthcheck
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lc.Append(fx.Hook{
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OnStart: func(_ context.Context) error {
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return nil
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},
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})
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return s, nil
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}
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func (s *Handlers) respondJSON(
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w http.ResponseWriter,
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_ *http.Request,
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data any,
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status int,
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) {
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w.Header().Set("Content-Type", jsonContentType)
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w.WriteHeader(status)
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if data != nil {
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err := json.NewEncoder(w).Encode(data)
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if err != nil {
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s.log.Error("json encode error", "error", err)
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}
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}
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}
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// decodeJSON decodes the request body into v. It returns errNotJSON,
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// reading nothing, unless the request's Content-Type is
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// application/json, with or without parameters such as charset. The
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// body is expected to already be bounded by the body-size middleware,
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// so a caller can distinguish an over-limit body from malformed JSON
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// by testing the returned error for *http.MaxBytesError.
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func (s *Handlers) decodeJSON(
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_ http.ResponseWriter,
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r *http.Request,
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v any,
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) error {
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// A page on another origin can POST text/plain or a form without
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// a CORS preflight, so its visitors' browsers would send it
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// whatever the CORS settings. A JSON POST waits for the
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// preflight, so only JSON is taken.
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mediaType, _, err := mime.ParseMediaType(r.Header.Get("Content-Type"))
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if err != nil || mediaType != "application/json" {
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return errNotJSON
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}
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return json.NewDecoder(r.Body).Decode(v)
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}
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