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//! Pagination strategies for REST APIs.
pub mod cursor;
pub mod link_header;
pub mod next_link_body;
pub mod offset;
pub mod page;
use faucet_core::FaucetError;
use reqwest::header::HeaderMap;
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};
use serde_json::Value;
use std::collections::HashMap;
/// Supported pagination strategies.
#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
#[serde(tag = "type")]
pub enum PaginationStyle {
None,
Cursor {
next_token_path: String,
param_name: String,
},
LinkHeader,
/// The full URL of the next page is embedded in the response body.
/// `next_link_path` is a JSONPath expression pointing to that URL field
/// (e.g. `"$.next_link"`). Pagination stops when the field is absent,
/// null, or an empty string.
NextLinkInBody {
next_link_path: String,
},
PageNumber {
param_name: String,
start_page: usize,
page_size: Option<usize>,
page_size_param: Option<String>,
},
Offset {
offset_param: String,
limit_param: String,
limit: usize,
total_path: Option<String>,
},
}
/// Internal state tracked across pages.
#[derive(Debug, Default)]
pub struct PaginationState {
pub page: usize,
pub next_token: Option<String>,
pub offset: usize,
pub next_link: Option<String>,
/// The previous page's token/link, used for loop detection.
/// If `advance()` produces the same value twice in a row, pagination
/// is stuck and we stop rather than looping forever.
#[doc(hidden)]
pub previous_token: Option<String>,
/// Fingerprint of the previous page's body, used by `PageNumber` loop
/// detection: APIs that clamp an out-of-range page to the last page and
/// re-return it (non-empty) would otherwise loop until `max_pages`.
#[doc(hidden)]
pub previous_page_fingerprint: Option<u64>,
/// Set by [`PaginationStyle::advance`] when the body-fingerprint stagnation
/// guard fires: the page just handed to `advance` is a duplicate of the
/// previous one and the caller must **drop** it rather than emit it a second
/// time (audit #321 L1). Only the content-stagnation guards set it; a normal
/// last-page stop leaves it `false` so the final page is still emitted.
#[doc(hidden)]
pub current_page_is_duplicate: bool,
}
/// Cheap, stable fingerprint of a response body for content-stagnation
/// loop detection.
fn body_fingerprint(body: &Value) -> u64 {
use std::hash::{Hash, Hasher};
let mut h = std::collections::hash_map::DefaultHasher::new();
body.to_string().hash(&mut h);
h.finish()
}
impl PaginationStyle {
pub fn apply_params(&self, params: &mut HashMap<String, String>, state: &PaginationState) {
match self {
PaginationStyle::None => {}
PaginationStyle::Cursor { param_name, .. } => {
cursor::apply_params(params, param_name, &state.next_token);
}
PaginationStyle::LinkHeader => {}
PaginationStyle::NextLinkInBody { .. } => {}
PaginationStyle::PageNumber {
param_name,
start_page,
page_size,
page_size_param,
} => {
page::apply_params(
params,
param_name,
*start_page,
state.page,
*page_size,
page_size_param.as_deref(),
);
}
PaginationStyle::Offset {
offset_param,
limit_param,
limit,
..
} => {
offset::apply_params(params, offset_param, limit_param, state.offset, *limit);
}
}
}
/// Advance pagination state based on the response body and headers.
/// Returns `true` if there is a next page to fetch.
///
/// Includes **loop detection**: if a cursor or next-link value is identical
/// to the previous page's value, pagination stops with a warning instead of
/// looping forever.
pub fn advance(
&self,
body: &Value,
headers: &HeaderMap,
state: &mut PaginationState,
record_count: usize,
) -> Result<bool, FaucetError> {
match self {
PaginationStyle::None => Ok(false),
PaginationStyle::Cursor {
next_token_path, ..
} => {
let has_next = cursor::advance(body, next_token_path, &mut state.next_token)?;
if has_next {
if state.next_token == state.previous_token {
tracing::warn!(
"pagination loop detected: cursor {:?} repeated — stopping",
state.next_token
);
return Ok(false);
}
state.previous_token = state.next_token.clone();
}
Ok(has_next)
}
PaginationStyle::LinkHeader => match link_header::extract_next_link(headers) {
Some(link) => {
if Some(&link) == state.previous_token.as_ref() {
tracing::warn!(
"pagination loop detected: link {link:?} repeated — stopping"
);
state.next_link = None;
return Ok(false);
}
state.previous_token = Some(link.clone());
state.next_link = Some(link);
Ok(true)
}
None => {
state.next_link = None;
Ok(false)
}
},
PaginationStyle::NextLinkInBody { next_link_path } => {
let has_next = next_link_body::advance(body, next_link_path, &mut state.next_link)?;
if has_next {
if state.next_link == state.previous_token {
tracing::warn!(
"pagination loop detected: next_link {:?} repeated — stopping",
state.next_link
);
return Ok(false);
}
state.previous_token = state.next_link.clone();
}
Ok(has_next)
}
PaginationStyle::PageNumber { .. } => {
state.page += 1;
if record_count == 0 {
return Ok(false);
}
// Content-stagnation guard: some APIs clamp an out-of-range
// page to the last page and return it again (non-empty), which
// would loop until `max_pages` and duplicate records. Stop if
// this page's body is identical to the previous one (#78/#15).
let fp = body_fingerprint(body);
if state.previous_page_fingerprint == Some(fp) {
tracing::warn!(
"pagination loop detected: PageNumber returned an identical page — stopping"
);
// The current page IS the duplicate — signal the caller to
// drop it rather than emit it a second time (#321 L1).
state.current_page_is_duplicate = true;
return Ok(false);
}
state.previous_page_fingerprint = Some(fp);
Ok(true)
}
PaginationStyle::Offset {
limit, total_path, ..
} => {
let has_next = offset::advance(
body,
&mut state.offset,
record_count,
*limit,
total_path.as_deref(),
)?;
// Content-stagnation guard (#264 F18): a server that ignores
// the `offset` parameter re-returns the identical first page
// forever. With `total_path` absent (commonly omitted) the
// record-count heuristic keeps `has_next` true on every full
// page, so the run would loop until `max_pages`, duplicating
// records to the sink. Mirror the PageNumber guard: stop if
// this page's body is identical to the previous one. A
// zero-record / short page has already returned `false` above,
// so this only fires on a genuinely repeated full page.
//
// Scoped to `total_path.is_none()`: when `total_path` is set,
// `offset::advance` has an authoritative stop condition (offset
// reaches total), and a paging-metadata body that legitimately
// repeats (e.g. `{"total": N}` echoed on every page) must not
// be mistaken for stagnation.
if has_next && total_path.is_none() {
let fp = body_fingerprint(body);
if state.previous_page_fingerprint == Some(fp) {
tracing::warn!(
"pagination loop detected: Offset returned an identical page \
(server likely ignoring the offset parameter) — stopping"
);
// Drop this duplicate page rather than emit it (#321 L1).
state.current_page_is_duplicate = true;
return Ok(false);
}
state.previous_page_fingerprint = Some(fp);
}
Ok(has_next)
}
}
}
}