import Blob "mo:core/Blob";
import Nat "mo:core/Nat";
import Text "mo:core/Text";
import IC "ic:aaaaa-aa";
import Call "mo:ic/Call";

persistent actor {

  // Transform function: strips headers so all replicas see the same response for consensus.
  // MUST be a `shared query` function.
  public query func transform({
    context : Blob;
    response : IC.http_request_result;
  }) : async IC.http_request_result {
    {
      response with headers = []; // Strip headers -- they often contain non-deterministic values
    };
  };

  // GET request: fetch a JSON API
  public func getIcpPriceUsd() : async Text {
    let url = "https://api.coingecko.com/api/v3/simple/price?ids=internet-computer&vs_currencies=usd";

    let request : IC.http_request_args = {
      url = url;
      max_response_bytes = ?(10_000 : Nat64); // Always set — omitting defaults to 2MB and charges accordingly
      headers = [
        { name = "User-Agent"; value = "ic-canister" },
      ];
      body = null;
      method = #get;
      transform = ?{
        function = transform;
        context = Blob.fromArray([]);
      };
      is_replicated = null;
    };

    // Call.httpRequest computes and attaches the required cycles automatically
    let response = await Call.httpRequest(request);

    switch (Text.decodeUtf8(response.body)) {
      case (?text) { text };
      case (null) { "Response is not valid UTF-8" };
    };
  };

  // POST transform: also discards the body because httpbin.org includes the
  // sender's IP in the "origin" field, which differs across replicas.
  public query func transformPost({
    context : Blob;
    response : IC.http_request_result;
  }) : async IC.http_request_result {
    {
      response with
      headers = [];
      body = Blob.fromArray([]);
    };
  };

  // POST request: send JSON data
  public func postData(jsonPayload : Text) : async Text {
    let url = "https://httpbin.org/post";

    let request : IC.http_request_args = {
      url = url;
      max_response_bytes = ?(50_000 : Nat64);
      headers = [
        { name = "Content-Type"; value = "application/json" },
        { name = "User-Agent"; value = "ic-canister" },
        // Idempotency key: prevents duplicate processing if multiple replicas hit the endpoint
        { name = "Idempotency-Key"; value = "unique-request-id-12345" },
      ];
      body = ?Text.encodeUtf8(jsonPayload);
      method = #post;
      transform = ?{
        function = transformPost;
        context = Blob.fromArray([]);
      };
      is_replicated = null;
    };

    // Call.httpRequest computes and attaches the required cycles automatically
    let response = await Call.httpRequest(request);

    if (response.status == 200) {
      "POST successful (status 200)";
    } else {
      "POST failed with status " # Nat.toText(response.status);
    };
  };
};

undefined

```rust
use ic_cdk::api::canister_self;
use ic_cdk::management_canister::{
    http_request, HttpHeader, HttpMethod, HttpRequestArgs, HttpRequestResult,
    TransformArgs, TransformContext, TransformFunc,
};
use ic_cdk::{query, update};
use serde::Deserialize;

/// Transform function: strips non-deterministic headers so all replicas agree.
/// MUST be a #[query] function.
#[query(hidden = true)]
fn transform(args: TransformArgs) -> HttpRequestResult {
    HttpRequestResult {
        status: args.response.status,
        body: args.response.body,
        headers: vec![], // Strip all headers for consensus
        // If you need specific headers, filter them here:
        // headers: args.response.headers.into_iter()
        //     .filter(|h| h.name.to_lowercase() == "content-type")
        //     .collect(),
    }
}

/// GET request: Fetch JSON from an external API
#[update]
async fn fetch_price() -> String {
    let url = "https://api.coingecko.com/api/v3/simple/price?ids=internet-computer&vs_currencies=usd";

    let request = HttpRequestArgs {
        url: url.to_string(),
        max_response_bytes: Some(10_000),
        method: HttpMethod::GET,
        headers: vec![
            HttpHeader {
                name: "User-Agent".to_string(),
                value: "ic-canister".to_string(),
            },
        ],
        body: None,
        transform: Some(TransformContext {
            function: TransformFunc::new(canister_self(), "transform".to_string()),
            context: vec![],
        }),
        is_replicated: None,
    };

    // http_request calls automatically attaches the required cycles
    match http_request(&request).await {
        Ok(response) => {
            let body = String::from_utf8(response.body)
                .unwrap_or_else(|_| "Invalid UTF-8 in response".to_string());

            if response.status != candid::Nat::from(200u64) {
                return format!("HTTP error: status {}", response.status);
            }

            body
        }
        Err(err) => {
            format!("HTTP outcall failed: {:?}", err)
        }
    }
}

/// Typed response parsing example
#[derive(Deserialize)]
struct PriceResponse {
    #[serde(rename = "internet-computer")]
    internet_computer: PriceData,
}

#[derive(Deserialize)]
struct PriceData {
    usd: f64,
}

#[update]
async fn get_icp_price_usd() -> String {
    let body = fetch_price().await;

    match serde_json::from_str::<PriceResponse>(&body) {
        Ok(parsed) => format!("ICP price: ${:.2}", parsed.internet_computer.usd),
        Err(e) => format!("Failed to parse price response: {}", e),
    }
}

/// POST transform: strips headers AND body because httpbin.org includes the
/// sender's IP in the "origin" field, which differs across replicas.
#[query(hidden = true)]
fn transform_post(args: TransformArgs) -> HttpRequestResult {
    HttpRequestResult {
        status: args.response.status,
        body: vec![],
        headers: vec![],
    }
}

/// POST request: Send JSON data to an external API
#[update]
async fn post_data(json_payload: String) -> String {
    let url = "https://httpbin.org/post";

    let request = HttpRequestArgs {
        url: url.to_string(),
        max_response_bytes: Some(50_000),
        method: HttpMethod::POST,
        headers: vec![
            HttpHeader {
                name: "Content-Type".to_string(),
                value: "application/json".to_string(),
            },
            HttpHeader {
                name: "User-Agent".to_string(),
                value: "ic-canister".to_string(),
            },
            // Idempotency key: prevents duplicate processing across replicas
            HttpHeader {
                name: "Idempotency-Key".to_string(),
                value: "unique-request-id-12345".to_string(),
            },
        ],
        body: Some(json_payload.into_bytes()),
        transform: Some(TransformContext {
            function: TransformFunc::new(canister_self(), "transform_post".to_string()),
            context: vec![],
        }),
        is_replicated: None,
    };

    // http_request automatically attaches the required cycles
    match http_request(&request).await {
        Ok(response) => {
            if response.status == candid::Nat::from(200u64) {
                "POST successful (status 200)".to_string()
            } else {
                format!("POST failed with status {}", response.status)
            }
        }
        Err(err) => {
            format!("HTTP outcall failed: {:?}", err)
        }
    }
}

Base cost:                      49_140_000 cycles  (= (3_000_000 + 60_000*13) * 13)
+ per request byte:              5_200 cycles      (= 400 * 13)
+ per max_response_bytes byte:  10_400 cycles      (= 800 * 13)

IMPORTANT: The charge is against max_response_bytes, NOT actual response size.
If you omit max_response_bytes, the system assumes 2MB and charges ~21.5B cycles.

undefined

Note: HTTPS outcalls work on the local replica. icp-cli proxies the requests through the local HTTP gateway.

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#[query]
fn transform_normalize(args: TransformArgs) -> HttpRequestResult {
    // Parse and re-serialize to normalize field ordering
    let body = if let Ok(json) = serde_json::from_slice::<serde_json::Value>(&args.response.body) {
        serde_json::to_vec(&json).unwrap_or(args.response.body)
    } else {
        args.response.body
    };

    HttpRequestResult {
        status: args.response.status,
        body,
        headers: vec![],
    }
}