Azure table storage API inconsistent replies - azure

Question

I have an http-triggered azure function that receives a zip code. It then queries an Azure Table using the table API and retrieves the city, state, etc. The table contains zip/postal codes for US and CAN so there's about a million rows. When I send a request it returns the correct value the first time but if I keep sending it over and over it randomly switches between returning the record and returning an empty set. So it's not failing, and I'm not getting any kind of error like a timeout.
here is an example of a successful reply:
{
odata.metadata: "https://storageaccount###.table.core.windows.net/$metadata#Table###",
value: [
{
odata.etag: "W/"datetime'2019-10-18T16%3A02%3A26.9420514Z'"",
PartitionKey: "Portsmouth",
RowKey: "00210",
Timestamp: "2019-10-18T16:02:26.9420514Z",
AreaCode: "603",
City: "Portsmouth",
Country: "US",
Pref: "P",
State: "NH",
Zip: "00210"
}
]
}
and here is an empty one after pressing F5 after getting above reply:
{
odata.metadata: "https://storageaccount###.table.core.windows.net/$metadata#Table###",
value: [ ]
}
And then if I keep pressing F5 sometimes I get the record and sometimes I don't.
here are the table api url parameters (SAS-minus the signature)
?$filter=RowKey eq '00210' and Country eq 'US'
&sv=2019-02-02
&ss=t
&srt=sco
&sp=r
&se=2099-10-18T05:27:30Z
&st=2019-10-17T21:27:30Z
&spr=https
Does anyone know why it's behaving this way or what I could look into to figure it out?
According to this page there is a 5 second timeout for querying azure tables
(https://learn.microsoft.com/en-us/rest/api/storageservices/query-timeout-and-pagination). but when I look at the headers in postman I don't see any tokens.
postman results: https://i.stack.imgur.com/hReDM.png
full CORRECTED code
public static async Task<string> Run(HttpRequest req, ILogger log)
{
log.LogInformation("Start time = "+ DateTime.Now);
string apiResponse = "";
string zip = req.Query["zip"];
if(string.IsNullOrEmpty(zip)){return "No zip code found - please provide a url parameter in the format 'zip=[code]'";}
string apiBaseUrl = "https://***storage.table.core.windows.net/zip**?";
string queryFilter = "$first&$filter=RowKey eq '" + zip + "'";
//generate auth url in storage account in Azure
string authorization = "&sv=2019-02-02&ss=t&srt=sco&sp=r&se=2099-10-18T00:38:11Z&st=2019-10-17T16:38:11Z&spr=https&sig=7S%2BkaiTwGsZIkL***";
Regex rx_US = new Regex(#"^\d{5}$");
Regex rx_CA = new Regex(#"^[A-Za-z]\d[A-Za-z][ -]?\d[A-Za-z]\d$");
if (rx_US.IsMatch(zip))
{
queryFilter = queryFilter + " and Country eq 'US'";
}
else if (rx_CA.IsMatch(zip))
{
//the table search is case sensitive - test for common errors
zip = zip.ToUpper(); //make all upper case
Regex rx_CA1 = new Regex(#"^[A-Z]\d[A-Z]-\d[A-Z]\d$"); //dash
Regex rx_CA2 = new Regex(#"^[A-Z]\d[A-Z]\d[A-Z]\d$"); //no space
if (rx_CA1.IsMatch(zip)){zip = zip.Replace("-", " ");}
if (rx_CA2.IsMatch(zip)){zip = zip.Insert (3, " ");}
queryFilter = "$single&$filter=RowKey eq '" + zip + "'" + " and Country eq 'CA'";
}
string queryUrl = apiBaseUrl + queryFilter + authorization;
try
{
var httpWebRequest = WebRequest.Create(queryUrl);
httpWebRequest.ContentType = "application/json";
httpWebRequest.Headers.Add("Accept","application/json"); //if this is omitted you will get xml format
httpWebRequest.Method = "GET";
var httpResponse = await httpWebRequest.GetResponseAsync();
using(var streamReader = new StreamReader(httpResponse.GetResponseStream()))
{
var responseText = streamReader.ReadToEnd();
apiResponse = responseText;
log.LogInformation("Full Table Response = " + responseText);
}
int i = 0;
while (httpResponse.Headers["x-ms-continuation-NextPartitionKey"] != null && apiResponse.Length < 105)
{
//if response is > 105 then it found something - don't keep looking
//if there are continuation tokens then keep querying until you find something
var partitionToken = httpResponse.Headers["x-ms-continuation-NextPartitionKey"];
var rowToken = httpResponse.Headers["x-ms-continuation-NextRowKey"];
var continuationUrl = "NextPartitionKey="+partitionToken+"&NextRowKey="+rowToken+"&";
queryUrl = apiBaseUrl + continuationUrl + queryFilter + authorization;
log.LogInformation("begin new httpRequest...");
httpWebRequest = WebRequest.Create(queryUrl);
httpWebRequest.ContentType = "application/json";
httpWebRequest.Headers.Add("Accept","application/json");
httpWebRequest.Method = "GET";
httpResponse = await httpWebRequest.GetResponseAsync();
using(var streamReader = new StreamReader(httpResponse.GetResponseStream()))
{
var responseText = streamReader.ReadToEnd();
apiResponse = responseText;
log.LogInformation("Full Table Response = " + responseText);
}
i++;
log.LogInformation("loop # "+ i + " - url = " + queryUrl + " Response = "+ apiResponse);
}
if(apiResponse.Length > 105)
{
//strip out extra data
apiResponse = apiResponse.Remove(1,101);
apiResponse = apiResponse.Remove(apiResponse.Length - 2,2);
}
else
{
apiResponse = "No data found for zip = " + zip + " - Ensure you have proper format and case";
}
}
catch (Exception ex)
{
apiResponse = "error: " + ex.Message;
}
log.LogInformation("ZipPostal function completed and returned "+ apiResponse);
return apiResponse;
}