internal/gcp/gemini/testdata/generatetext.httprr

httprr trace v1
769 6393
POST https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-pro:generateContent HTTP/1.1
Host: generativelanguage.googleapis.com
User-Agent: gemini httprecord
Content-Length: 540
Content-Type: application/json

{"contents":[{"parts":[{"text":"CanonicalHeaderKey returns the canonical format of the header key s. The canonicalization converts the first letter and any letter following a hyphen to upper case; the rest are converted to lowercase. For example, the canonical key for 'accept-encoding' is 'Accept-Encoding'. If s contains a space or invalid header field bytes, it is returned without modifications."},{"text":"When should I use CanonicalHeaderKey?"}],"role":"user"}],"generationConfig":{"candidateCount":1,"responseMimeType":"text/plain"}}HTTP/2.0 200 OK
Alt-Svc: h3=":443"; ma=2592000,h3-29=":443"; ma=2592000
Content-Type: application/json; charset=UTF-8
Date: Fri, 03 Oct 2025 15:37:17 GMT
Server: scaffolding on HTTPServer2
Server-Timing: gfet4t7; dur=31480
Vary: Origin
Vary: X-Origin
Vary: Referer
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-Xss-Protection: 0

{
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            "text": "Excellent question. You've perfectly described *what* `CanonicalHeaderKey` does. The question of *when* to use it gets to the core of how Go's `net/http` package is designed.\n\nThe short answer is: **You almost never need to call `CanonicalHeaderKey` yourself.** The Go standard library's `http.Header` type calls it for you automatically.\n\nTo understand why, let's break down the problem it solves.\n\n### The Problem: Case-Insensitive Headers\n\nAccording to the HTTP specification (RFC 7230), header field names are **case-insensitive**. This means that the following headers are all semantically identical:\n\n*   `Content-Type`\n*   `content-type`\n*   `CONTENT-TYPE`\n*   `cOnTeNt-TyPe`\n\nThis presents a challenge for programming languages. If you want to store headers in a standard data structure like a map (or a dictionary), how do you handle these different casings? If you use the key as-is, you could end up with multiple entries for what is supposed to be the same header:\n\n```go\n// A naive map would treat these as different entries\nheaders := map[string]string{\n    \"content-type\": \"application/json\",\n    \"Content-Type\": \"text/html\", // This would overwrite the previous one in Go, but illustrates the lookup problem\n}\n```\nLooking up `headers[\"CONTENT-TYPE\"]` would fail to find the entry. This is unreliable and buggy.\n\n### The Solution: Canonicalization\n\nTo solve this, a program must choose one single, consistent format for all header keys. This standard format is called the **canonical form**.\n\nGo's `net/http` package chose the format you described: `Accept-Encoding` (first letter and any letter after a hyphen is capitalized). The `CanonicalHeaderKey` function is the tool that enforces this standard.\n\n### How `http.Header` Uses It Internally\n\nThe `http.Header` type in Go (which you find in `http.Request.Header` and `http.Response.Header`) is defined as `type Header map[string][]string`.\n\nWhenever you interact with an `http.Header` object using its methods, it automatically canonicalizes the key for you.\n\n*   `header.Set(\"content-type\", \"application/json\")`\n*   `header.Add(\"X-CUSTOM-HEADER\", \"value1\")`\n*   `value := header.Get(\"host\")`\n*   `header.Del(\"ACCEPT-ENCODING\")`\n\nIn all of these examples, the methods (`Set`, `Add`, `Get`, `Del`) will first pass the key (`\"content-type\"`, `\"X-CUSTOM-HEADER\"`, etc.) to `CanonicalHeaderKey` before performing the map operation.\n\nThis ensures that no matter how you write the header name, it is always stored and retrieved consistently.\n\n```go\nimport (\n    \"fmt\"\n    \"net/http\"\n)\n\nfunc main() {\n    h := make(http.Header)\n\n    // Set a header with a non-canonical key\n    h.Set(\"content-type\", \"application/json\")\n    \n    // Add another header with a strange casing\n    h.Add(\"x-ReQuEsT-iD\", \"12345\")\n\n    fmt.Println(\"Header map after setting:\")\n    fmt.Printf(\"%#v\\n\\n\", h)\n\n    // Get the header using yet another casing\n    contentType := h.Get(\"Content-Type\")\n    fmt.Printf(\"Got Content-Type: %s\\n\", contentType)\n\n    requestId := h.Get(\"x-request-id\")\n    fmt.Printf(\"Got X-Request-Id: %s\\n\", requestId)\n}\n```\n\n**Output:**\n```\nHeader map after setting:\nhttp.Header{\"Content-Type\":[]string{\"application/json\"}, \"X-Request-Id\":[]string{\"12345\"}}\n\nGot Content-Type: application/json\nGot X-Request-Id: 12345\n```\nAs you can see, the keys stored in the map are `\"Content-Type\"` and `\"X-Request-Id\"`, their canonical forms.\n\n---\n\n### So, When Should I Use It?\n\nYou should only call `CanonicalHeaderKey` directly in the rare cases where you are **working with HTTP headers outside of the standard `http.Header` type**.\n\nHere are a few potential scenarios:\n\n1.  **Implementing a Custom Header Type:** If for some reason you are creating your own header storage mechanism (e.g., a custom proxy or a library that needs to manipulate raw headers) and want it to be compatible with the behavior of Go's standard library.\n\n    ```go\n    // You're building your own header map for a specific reason\n    myHeaders := make(map[string]string)\n    rawKey := \"x-powered-by\"\n    \n    // To be consistent with Go's standard library, you canonicalize the key\n    canonicalKey := http.CanonicalHeaderKey(rawKey) // Returns \"X-Powered-By\"\n    myHeaders[canonicalKey] = \"My-Awesome-Framework\"\n    ```\n\n2.  **Interacting with External Systems:** If you receive a set of headers as a simple `map[string]string` from another system (like a configuration file or a message queue payload) and need to convert it into a standard `http.Header`.\n\n3.  **Logging or Debugging:** You might use it to normalize header keys for consistent and clean log output.\n\n### In Summary\n\n| Situation | Should you use `CanonicalHeaderKey`? | Why? |\n| :--- | :--- | :--- |\n| **Working with `http.Request.Header` or `http.Response.Header`** | **No** | The `Get`, `Set`, `Add`, and `Del` methods already do it for you. Calling it yourself is redundant. |\n| **Creating your own `http.Header` object** | **No** | Same as above. The methods on the type handle it. |\n| **Building a custom system that manipulates raw headers** | **Yes** | Use it to ensure your system behaves consistently with Go's standard library and the HTTP spec. |\n| **Normalizing header keys for logging or display** | **Yes** | It's a useful utility for ensuring consistent string formatting of header keys. |"
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