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Propagate runtime ID across API requests

Quick Overview

This question evaluates proficiency in runtime ID propagation across HTTP requests, JSON parsing and serialization, nested data traversal, and type-preserving replacement in request URLs and bodies; it is categorized under Coding & Algorithms and focuses on practical application rather than purely conceptual understanding.

Company: Stripe

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Technical Screen

## Debug chained API requests by propagating a runtime ID You are given a sequence of **5 API requests** that must be executed in order. - Request 1 (a `POST`) succeeds and returns `200 OK` with a JSON response containing a newly created resource ID. - Requests 2–5 currently fail because they incorrectly use a **hardcoded** ID (e.g., `"123"`) in their **URL path and/or JSON body** instead of the ID returned by Request 1. ### Task Write a function that, given: 1. `requests`: a list of request objects in execution order. Each request has: - `method` (string) - `url` (string) - `headers` (map of string → string) - `body` (either `null`, a JSON object, or a JSON string) 2. `first_response_body`: the parsed JSON body returned by Request 1, which includes the runtime ID (for example under `id`) 3. `old_id`: the hardcoded ID value currently present in later requests returns a **new list of requests** where, for Requests 2–5: - Every occurrence of `old_id` in the request **URL** is replaced with the runtime ID from `first_response_body`. - Every occurrence of `old_id` anywhere inside the request **body** (including nested fields, arrays, and string values) is replaced with the runtime ID. ### Requirements / Notes - Do **not** modify Request 1. - The runtime ID may be numeric or string; preserve the correct type when updating JSON bodies. - The request body may be `null`, a JSON object, or a JSON string (in which case you should parse it, modify it, then serialize it back). - Assume all requests are well-formed; focus on correct propagation and replacement. ### Output Return the updated list of request objects.

Quick Answer: This question evaluates proficiency in runtime ID propagation across HTTP requests, JSON parsing and serialization, nested data traversal, and type-preserving replacement in request URLs and bodies; it is categorized under Coding & Algorithms and focuses on practical application rather than purely conceptual understanding.

You are given exactly 5 API request objects that are executed in order. Request 1 creates a resource and its parsed response body contains the runtime resource ID at key 'id'. Requests 2 through 5 currently use a hardcoded ID in their URL path and/or JSON body. Return a new list of requests where Request 1 is unchanged, and Requests 2 through 5 have every occurrence of the hardcoded ID replaced by the runtime ID. URL replacement is string-based. Body replacement must recursively process dictionaries, arrays, object keys, and scalar values. If a JSON scalar value is exactly the hardcoded ID, replace it with the runtime ID value itself so the runtime ID type is preserved. If the hardcoded ID appears inside a longer string, replace that substring with str(runtime_id). If a body is a JSON string, parse it, update it, then serialize it back as compact JSON with sorted keys.

Constraints

len(requests) == 5
first_response_body contains key 'id'
old_id is a non-empty string or integer
Each request body is None, a JSON-like Python object, or a valid JSON string
Total number of nested body values across all requests is at most 10000
Headers are not modified

Examples

Input: ([{'method':'POST','url':'/widgets','headers':{'Content-Type':'application/json'},'body':{'name':'demo'}},{'method':'GET','url':'/widgets/123','headers':{},'body':None},{'method':'PATCH','url':'/widgets/123','headers':{},'body':{'id':'123','name':'updated','tags':['owner-123','123']}},{'method':'POST','url':'/widgets/123/links','headers':{},'body':'{"targetId":"123","note":"link-to-123"}'},{'method':'DELETE','url':'/widgets/123','headers':{},'body':{}}], {'id':'abc-999'}, '123')

Expected Output: [{'method':'POST','url':'/widgets','headers':{'Content-Type':'application/json'},'body':{'name':'demo'}},{'method':'GET','url':'/widgets/abc-999','headers':{},'body':None},{'method':'PATCH','url':'/widgets/abc-999','headers':{},'body':{'id':'abc-999','name':'updated','tags':['owner-abc-999','abc-999']}},{'method':'POST','url':'/widgets/abc-999/links','headers':{},'body':'{"note":"link-to-abc-999","targetId":"abc-999"}'},{'method':'DELETE','url':'/widgets/abc-999','headers':{},'body':{}}]

Explanation: Requests 2 through 5 use the runtime ID in URLs. Nested body values and substrings are also updated. The JSON string body is parsed and serialized back with sorted keys.

Input: ([{'method':'POST','url':'/orders','headers':{},'body':{'templateId':'123','keep':'request1 uses 123 but unchanged'}},{'method':'PUT','url':'/orders/123','headers':{},'body':{'parentId':'123','quantity':123,'nested':{'child':'child-123'}}},{'method':'POST','url':'/orders/123/items/123','headers':{},'body':{'items':[{'resourceId':'123'},{'resourceId':123},{'label':'order-123'}]}},{'method':'PATCH','url':'/orders/123/status','headers':{},'body':'{"id":"123","ids":["123",123],"message":"123 done"}'},{'method':'GET','url':'/orders/123/audit','headers':{},'body':None}], {'id':987}, '123')

Expected Output: [{'method':'POST','url':'/orders','headers':{},'body':{'templateId':'123','keep':'request1 uses 123 but unchanged'}},{'method':'PUT','url':'/orders/987','headers':{},'body':{'parentId':987,'quantity':987,'nested':{'child':'child-987'}}},{'method':'POST','url':'/orders/987/items/987','headers':{},'body':{'items':[{'resourceId':987},{'resourceId':987},{'label':'order-987'}]}},{'method':'PATCH','url':'/orders/987/status','headers':{},'body':'{"id":987,"ids":[987,987],"message":"987 done"}'},{'method':'GET','url':'/orders/987/audit','headers':{},'body':None}]

Explanation: The runtime ID is numeric, so exact body values like '123' and 123 become integer 987. Longer strings such as 'child-123' become 'child-987'. Request 1 is unchanged.

Input: ([{'method':'POST','url':'/resources/old','headers':{},'body':{'id':'old','note':'old in request1 stays'}},{'method':'GET','url':'/resources','headers':{},'body':None},{'method':'PUT','url':'/resources/old/old','headers':{},'body':{'emptyList':[],'emptyObj':{},'value':'no-match'}},{'method':'PATCH','url':'/resources/x','headers':{},'body':'{"items":[],"meta":{},"note":"nothing"}'},{'method':'DELETE','url':'/resources/old','headers':{},'body':{'ids':['old','prefix-old-suffix']}}], {'id':'new'}, 'old')

Expected Output: [{'method':'POST','url':'/resources/old','headers':{},'body':{'id':'old','note':'old in request1 stays'}},{'method':'GET','url':'/resources','headers':{},'body':None},{'method':'PUT','url':'/resources/new/new','headers':{},'body':{'emptyList':[],'emptyObj':{},'value':'no-match'}},{'method':'PATCH','url':'/resources/x','headers':{},'body':'{"items":[],"meta":{},"note":"nothing"}'},{'method':'DELETE','url':'/resources/new','headers':{},'body':{'ids':['new','prefix-new-suffix']}}]

Explanation: This covers empty bodies and empty nested containers. Request 1 contains the old ID but must remain unchanged. Duplicate URL occurrences are all replaced.

Input: ([{'method':'POST','url':'/things','headers':{},'body':{'id':42,'text':'42'}},{'method':'GET','url':'/things/42','headers':{},'body':None},{'method':'PATCH','url':'/things/42','headers':{},'body':{'id':42,'ref':'42','label':'thing-42','arr':[42,'42','x42x',False]}},{'method':'POST','url':'/things/42/actions','headers':{},'body':'{"number":42,"string":"42","mixed":"a42b","list":[42,"42"]}'},{'method':'DELETE','url':'/things/42','headers':{},'body':{}}], {'id':'r-007'}, 42)

Expected Output: [{'method':'POST','url':'/things','headers':{},'body':{'id':42,'text':'42'}},{'method':'GET','url':'/things/r-007','headers':{},'body':None},{'method':'PATCH','url':'/things/r-007','headers':{},'body':{'id':'r-007','ref':'r-007','label':'thing-r-007','arr':['r-007','r-007','xr-007x',False]}},{'method':'POST','url':'/things/r-007/actions','headers':{},'body':'{"list":["r-007","r-007"],"mixed":"ar-007b","number":"r-007","string":"r-007"}'},{'method':'DELETE','url':'/things/r-007','headers':{},'body':{}}]

Explanation: The old ID is numeric and the runtime ID is a string. Exact numeric and string ID values become the string runtime ID, while booleans are not treated as numbers.

Hints

Treat each request body as a JSON tree and recursively transform dictionaries, lists, and scalar values.
Use string replacement for URLs and longer string fragments, but replace exact JSON ID values with the runtime ID object itself to preserve its type.

Quick Overview